use of program_name

[Dave Love]

Gnulib routines call `error', and on a non-glibc system that's likely
to use an uninitialized `program_name' since the variable is
initialized in progname.c, and that's not required.  Users probably
won't find out about it until `error' gets called at some stage and
prints junk; if gnulib supports a library, that can't ensure it's set
anyway.

Shouldn't `program_name' be initialized in error.c instead (perhaps to
a more meaningful value than NULL)?

It could probably do with a note about this in gnulib.texi, but I
don't know whether the variable is meant to be set directly or only
through `set_program_name'.