Uglify Ti.Filesystem.getFile to maintain Titanium getFile API compatibility 

This change takes a more conservative approach to https://github.com/dbankier/TiShadow/pull/290,
It only changes Ti.Filesystem.getFile calls to use a new introduced method in PlatformRequire which adds "/" to path entries only if they are needed, and doesn't mask bugs that could be found if running directly without TiShadow.
Other usages of PlatformRequire.file are not changed in any way.
Test fixtures updated to reflect the change.