Fix a couple of minor warnings.

Just so that the build passes w/ -Werror
Merge pull request #64 from NiLuJe/fix-warning

Fix a couple of minor warnings.
Zip: Make Mac extension handling optional with "mac-ext" option for Zip, default true on Mac OS"
Fix: process directory entries even when mac extensions are turned off
Enable mac extensions for mac extension test
streaming zip reader does not support mac extensions
Return correct error when multiple modules match an option spec