Try to be more explicit about the newly allocated absolute path and
the relative offset and actually compare the relative part.

-get_full_path(const NS_tchar *relpath)
+new_absolute_path(const NS_tchar *relpath)

-get_relative_path(const NS_tchar *fullpath)
+get_relative_offset(const NS_tchar *abs_path)

Change-Id: I02abd722fc89a1688502b9c5cd375954f9f0bc05
Reviewed-on: https://gerrit.libreoffice.org/60168
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>