gpg: Allow --dearmor to decode all kinds of armor files.
* g10/filter.h (armor_filter_context_t): New fields dearmor_mode and dearmor_state. * g10/dearmor.c (dearmor_file): Set dearmor_mode. * g10/armor.c (is_armor_header): Magic to switch to generic dearmor mode. (parse_header_line): Treat non OpenPGP armor in a special way. (check_input): Ditto. (radix64_read): Detect non OpenPGP armor END lines.