unlinking symlinked directories and trailing slashes

Filesystem::removeDirectory() didn't detect all symlinked directories
properly due to not resolving pathnames with trailing slashes first.

this commit fixes that issue by resolving pathnames with trailing slashes
by removing those in case they are representing a symlinked directory.

#3144

Reference:

 A.4.12 Pathname Resolution - The Open Group Base Specifications Issue 7
 IEEE Std 1003.1, 2013 Edition Section
 <http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xbd_chap04.html>