steal more (good) stuff from mandoc-portable :)

HAVE_PROGRAM_INVOCATION_SHORT_NAME is always defined; look at wether it's zero or not.

was a mistake on my part and a leftover from the first iterations. Initially I only stole a few bits, that's why the comment but not the copyright, but then i threwed out and restarted using oconfigure. Then the configure script has its own independent changes, but need to give attribution nevertheless.

not just the number of lines, check the full page!