mysql - remove 'data' from prefix

Remove the 'data' folder from the prefix, so the setup script
will not try to create databases there. Putting databases
in the prefix instead of directly in /usr/local means they
get deleted on a MySQL update, which is not what you want.

Formula/mysql.rb

@@ -18,20 +18,17 @@ class Mysql < Formula
     ]
   end
 
-  def patches
-    DATA
-  end
+  def patches; DATA; end
 
   def install
-    args = [
-      ".",
-      "-DCMAKE_INSTALL_PREFIX='#{prefix}'",
-      "-DMYSQL_DATADIR='#{var}/mysql'",
-      "-DINSTALL_MANDIR='#{man}'",
-      "-DWITH_SSL=yes",
-      "-DDEFAULT_CHARSET='utf8'",
-      "-DDEFAULT_COLLATION='utf8_general_ci'",
-      "-DSYSCONFDIR='#{HOMEBREW_PREFIX}/etc'"]
+    args = [".",
+            "-DCMAKE_INSTALL_PREFIX=#{prefix}",
+            "-DMYSQL_DATADIR=#{var}/mysql",
+            "-DINSTALL_MANDIR=#{man}",
+            "-DWITH_SSL=yes",
+            "-DDEFAULT_CHARSET=utf8",
+            "-DDEFAULT_COLLATION=utf8_general_ci",
+            "-DSYSCONFDIR=#{etc}"]
 
     # To enable unit testing at build, we need to download the unit testing suite
     args << "-DWITH_UNIT_TESTS=OFF" if not ARGV.include? '--with-tests'
@@ -48,6 +45,10 @@ class Mysql < Formula
     system "make install"
 
     (prefix+'com.mysql.mysqld.plist').write startup_plist
+
+    # Don't create databases inside of the prefix!
+    # See: https://github.com/mxcl/homebrew/issues/4975
+    rm_rf prefix+'data'
   end
 
   def caveats; <<-EOS.undent