rm without -f: give a better diagnostic when euidaccess fails.

rm without -f: give a better diagnostic when euidaccess fails.
* src/remove.c (write_protected_non_symlink): Return int, not bool,
so that we can indicate failure too (as a postive error number).
(prompt): If write_protected_non_symlink fails, report that error
number and fail rather than charging ahead and removing the dubious
entry.  Redo the logic of printing a diagnostic so that we need to
invoke quote (full_filename (...)) only once.  More details at:
<http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/9952/focus=9996>