posgresql: restore Python arch check

The Python arch check in the Postgres formula was changed to use the new python
helper. This was incorrect. We specifically want to check for a 32-bit python
located in /Library.

Formula/postgresql.rb

@@ -60,7 +60,7 @@ def install
       ENV.append 'LIBS', `uuid-config --libs`.strip
     end
 
-    if not build.build_32_bit? and MacOS.prefer_64_bit? and build.with? 'python'
+    if build.with? 'python' and MacOS.prefer_64_bit? and not build.build_32_bit?
       args << "ARCHFLAGS='-arch x86_64'"
       check_python_arch
     end
@@ -75,24 +75,23 @@ def install
   end
 
   def check_python_arch
-    # On 64-bit systems, we need to avoid a 32-bit Framework Python.
-    if python.framework?
-      unless archs_for_command(python.binary).include? :x86_64
-        opoo "Detected a framework Python that does not have 64-bit support in:"
-        puts <<-EOS.undent
-          #{python.prefix}
-
-          The configure script seems to prefer this version of Python over any others,
-          so you may experience linker problems as described in:
-            http://osdir.com/ml/pgsql-general/2009-09/msg00160.html
-
-          To fix this issue, you may need to either delete the version of Python
-          shown above, or move it out of the way before brewing PostgreSQL.
-
-          Note that a framework Python in /Library/Frameworks/Python.framework is
-          the "MacPython" version, and not the system-provided version which is in:
-            /System/Library/Frameworks/Python.framework
-        EOS
+    # On 64-bit systems, we need to look for a 32-bit Framework Python.
+    # The configure script prefers this Python version, and if it doesn't
+    # have 64-bit support then linking will fail.
+    framework_python = Pathname.new("/Library/Frameworks/Python.framework/Versions/Current/Python")
+    return unless framework_python.exist?
+    unless (archs_for_command(framework_python)).include? :x86_64
+      opoo "Detected a framework Python that does not have 64-bit support in:"
+      puts <<-EOS.undent
+          #{framework_python}
+
+        The configure script seems to prefer this version of Python over any others,
+        so you may experience linker problems as described in:
+          http://osdir.com/ml/pgsql-general/2009-09/msg00160.html
+
+        To fix this issue, you may need to either delete the version of Python
+        shown above, or move it out of the way before brewing PostgreSQL.
+      EOS
       end
     end
   end