Make PyMySQL work inside App generated by py2app

Setting the 'optimize' level to 2 was causing pymysql imports to
fail. This sets the 'optimize' level to 1, which only results in
a 1 MB increase in size and solves the issue.
Merge pull request #147 from ethanwhite/fix-osx-pymysql

Make PyMySQL work inside App generated by py2app