Bazaar - add --system option to force use of /usr/bin/python

* brew install --system bzr to force use of system Python
* Warn if the Python being used to install is 2.7.x

Formula/bazaar.rb

@@ -12,7 +12,18 @@ class Bazaar <Formula
   end
 
   def install
-    ENV.prepend "PATH", "/System/Library/Frameworks/Python.framework/Versions/Current/bin", ":" if ARGV.include? "--system"
+    if ARGV.include? "--system"
+      ENV.prepend "PATH", "/System/Library/Frameworks/Python.framework/Versions/Current/bin", ":"
+    else
+      python_version = `python -c "import sys;print sys.version"`
+      if python_version[0,4] == "2.7."
+        opoo <<-EOS
+Bazaar might not yet work with Python 2.7.
+You can force an installation using the system Python by doing:
+  brew install bazaar --system
+EOS
+      end
+    end
 
     # Find the archs of the Python we are building against.
     # If the python includes PPC support, then don't use Intel-
@@ -25,6 +36,7 @@ class Bazaar <Formula
     man1.install gzip('man1/bzr.1')
 
     system "make"
+    inreplace "bzr", "#! /usr/bin/env python", "#!/usr/bin/python" if ARGV.include? "--system"
     libexec.install ['bzr', 'bzrlib']
 
     bin.mkpath