* src/gpgmetools.c (check_overwriting): Change return type from a
boolean to a char *.  If the file exists, offer the user the option to
select a different file.  Return the file that is actually used.
(gpa_fopen): Take an additional parameter, FILENAME_USED.  Save the
filename returned by check_overwriting there.  Update users.
(gpa_open_output): Likewise.