* src/engine-gpg.c (add_file_name_arg_or_data): New.
(gpg_decrypt): Use add_file_name_arg_or_data instead of add_data for the
ciphertext.
(gpg_verify): Use add_file_name_arg_or_data instead of add_data for the
signature and the signed text.
* tests/run-decrypt.c (show_usage): New option --direct-file-io.
(main): Parse new option. If option is given, then don't open input
file, create simple data object instead of data object from stream and
set input file name on input data.
* tests/run-verify.c (show_usage): New option --direct-file-io.
(main): Parse new option. If option is given, then don't open input
files, create simple data objects instead of data objects from stream
and set input file names on input data objects.