algorithm which will be used if available.
* encode.c (encode_crypt, encrypt_filter), sign.c (sign_file): Use new
select_algo_from_prefs feature to check if forcing an algorithm would
violate the recipient preferences.
* photoid.c (get_default_photo_command, show_photos): Use different
default viewers on different platforms. Currently we have Win 9x, Win NT
(2k, xp), Mac OSX, RISC OS, and "everybody else". These are #ifdefs as
much as possible to avoid clutter.
* g10.c (strusage, build_list), keyedit.c (show_prefs), main.h, misc.c
(compress_algo_to_string, check_compress_algo), pkclist.c
(algo_available), keygen.c (keygen_set_std_prefs): New algo_to_string and
check functions for compress algorithms.