Fix handling of extra include directories passed to the global check.

This was actually completely broken - we were checking a property which
was never in fact used.

Also did some small cleanup:
 - Tabs to whitespace
 - Use cmake_parse_arguments instead of passing list references around.
Merge pull request #4 from smspillaz/cppcheck-target-cmake.item_4

Fix handling of extra include directories passed to the global check.