skip file permission test if program remains readable (for cygwin)

On Cygwin files can be readable to users even when their permissions are
set to disallow any reading. Currently i suspect this is due to Win32
admin user privileges trumping cygwin restrictions. As such, a skip is the
best fix here.
Merge pull request #385 from wchristian/skip_on_broken_cygwin

skip file permission test if program remains readable (for cygwin)