Python requires -fwrapv for Decimal division

According to:

http://stackoverflow.com/questions/7590137/dividing-decimals-yields-invalid-results-in-python-2-5-to-2-7

the Python interpreter must be built with -fwrapv for proper Decimal division.

To test:

python -c "from decimal import Decimal; print Decimal(4) / Decimal(2)"

If built with -fwrapv, this yields 2.

Closes Homebrew/homebrew#10487.

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

Formula/python.rb

@@ -40,6 +40,10 @@ class Python < Formula
   skip_clean ['bin', 'lib']
 
   def install
+    # Python requires -fwrapv for proper Decimal division
+    # See: http://stackoverflow.com/questions/7590137/dividing-decimals-yields-invalid-results-in-python-2-5-to-2-7
+    ENV.append_to_cflags "-fwrapv"
+
     if build_framework? and ARGV.include? "--static"
       onoe "Cannot specify both framework and static."
       exit 99