python2/3: Harden against other pythons. Pip 1.2

- Unset PYTHONPATH and PYTHONHOME which would lead to install distribute and
  pip into the wrong python.
- For NCLT: Add to CPPFLAGS the path to zlib via -I because python's setup.py
  scans only these flags.
- '-Qunused-arguments' can be added after ENV.enable_warnings to reduce
  noise. The only thing which we must not add is the "-w" switch!
- For python.rb only: Pass "--no-user-cfg" to python setup.py and add --force
  when installing distribute and pip to ensure overwriting with the new ones.

Closes Homebrew/homebrew#14689.
Closes Homebrew/homebrew#14686.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/python.rb

@@ -21,8 +21,8 @@ class Distribute < Formula
 end
 
 class Pip < Formula
-  url 'http://pypi.python.org/packages/source/p/pip/pip-1.1.tar.gz'
-  sha1 '842c4e2aff3f016feea3c6e992c7fa96e49c9aa0'
+  url 'http://pypi.python.org/packages/source/p/pip/pip-1.2.tar.gz'
+  sha1 '7876f943cfbb0bbb725c2761879de2889c1fe93b'
 end
 
 class Python < Formula
@@ -62,6 +62,11 @@ class Python < Formula
   end
 
   def install
+    # Unset these so that installing pip and distribute puts them where we want
+    # and not into some other Python the user has installed.
+    ENV['PYTHONPATH'] = nil
+    ENV['PYTHONHOME'] = nil
+
     args = %W[
              --prefix=#{prefix}
              --enable-ipv6
@@ -72,6 +77,12 @@ class Python < Formula
 
     args << '--without-gcc' if ENV.compiler == :clang
 
+    # Further, Python scans all "-I" dirs but not "-isysroot", so we add
+    # the needed includes with "-I" here to avoid this err:
+    #     building dbm using ndbm
+    #     error: /usr/include/zlib.h: No such file or directory
+    ENV.append 'CPPFLAGS', "-I#{MacOS.sdk_path}/usr/include" unless MacOS::CLT.installed?
+
     # Don't use optimizations other than "-Os" here, because Python's distutils
     # remembers (hint: `python-config --cflags`) and reuses them for C
     # extensions which can break software (such as scipy 0.11 fails when
@@ -85,6 +96,7 @@ class Python < Formula
       # http://docs.python.org/devguide/setup.html#id8 suggests to disable some Warnings.
       ENV.append_to_cflags '-Wno-unused-value'
       ENV.append_to_cflags '-Wno-empty-body'
+      ENV.append_to_cflags '-Qunused-arguments'
     end
 
     if build.universal?
@@ -128,8 +140,8 @@ class Python < Formula
     EOF
 
     # Install distribute and pip
-    Distribute.new.brew { system "#{bin}/python", "setup.py", "install" }
-    Pip.new.brew { system "#{bin}/python", "setup.py", "install" }
+    Distribute.new.brew { system "#{bin}/python", "setup.py", "--no-user-cfg", "install", "--force" }
+    Pip.new.brew { system "#{bin}/python", "setup.py", "--no-user-cfg", "install", "--force" }
   end
 
   def caveats

Formula/python3.rb

@@ -53,6 +53,11 @@ class Python3 < Formula
   end
 
   def install
+    # Unset these so that installing pip and distribute puts them where we want
+    # and not into some other Python the user has installed.
+    ENV['PYTHONPATH'] = nil
+    ENV['PYTHONHOME'] = nil
+
     args = %W[--prefix=#{prefix}
              --enable-ipv6
              --datarootdir=#{share}
@@ -62,6 +67,12 @@ class Python3 < Formula
 
     args << '--without-gcc' if ENV.compiler == :clang
 
+    # Further, Python scans all "-I" dirs but not "-isysroot", so we add
+    # the needed includes with "-I" here to avoid this err:
+    #     building dbm using ndbm
+    #     error: /usr/include/zlib.h: No such file or directory
+    ENV.append 'CPPFLAGS', "-I#{MacOS.sdk_path}/usr/include" unless MacOS::CLT.installed?
+
     # Don't use optimizations other than "-Os" here, because Python's distutils
     # remembers (hint: `python-config --cflags`) and reuses them for C
     # extensions which can break software (such as scipy 0.11 fails when
@@ -75,6 +86,7 @@ class Python3 < Formula
       # http://docs.python.org/devguide/setup.html#id8 suggests to disable some Warnings.
       ENV.append_to_cflags '-Wno-unused-value'
       ENV.append_to_cflags '-Wno-empty-body'
+      ENV.append_to_cflags '-Qunused-arguments'
     end
 
     # Allow sqlite3 module to load extensions:
@@ -117,14 +129,14 @@ class Python3 < Formula
 
     # Install distribute for python3
     Distribute.new.brew do
-      system "#{bin}/python3.2", "setup.py", "install"
+      system "#{bin}/python3.2", "setup.py", "install", "--force"
       # Symlink to easy_install3 to match python3 command.
       unless (scripts_folder/'easy_install3').exist?
         ln_s scripts_folder/"easy_install", scripts_folder/"easy_install3"
       end
     end
     # Install pip-3.2 for python3
-    Pip.new.brew { system "#{bin}/python3.2", "setup.py", "install" }
+    Pip.new.brew { system "#{bin}/python3.2", "setup.py", "install", "--force" }
   end
 
   def caveats