makefile rule for running msgmerge

[Ben Pfaff]

The rule in po/automake.mk for running msgmerge looks like this:

    $(POFILES): $(POTFILE)
            $(MSGMERGE) $(top_srcdir)/$* $< -o $@

I don't think this makes sense.  This expands to:

    po/en_GB.po po/nl.po po/pt_BR.po: po/pspp.pot
            $(MSGMERGE) $(top_srcdir)/$* $< -o $@

which is an explicit rule, not an implicit rule.  According to
the GNU make manual, $* expands like this in an explicit rule:

     In an explicit rule, there is no stem; so `$*' cannot be determined
     in that way.  Instead, if the target name ends with a recognized
     suffix (*note Old-Fashioned Suffix Rules: Suffix Rules.), `$*' is
     set to the target name minus the suffix.  For example, if the
     target name is `foo.c', then `$*' is set to `foo', since `.c' is a
     suffix.  GNU `make' does this bizarre thing only for compatibility
     with other implementations of `make'.  You should generally avoid
     using `$*' except in implicit rules or static pattern rules.

     If the target name in an explicit rule does not end with a
     recognized suffix, `$*' is set to the empty string for that rule.

so $* will either be something like po/en_GB or even the empty
string here.  I've seen the former in some runs; I'm not sure
I've seen the latter.  But neither one makes sense to me.

Also, POSIX says $< and $@ are defined only for implicit rules,
but I don't think that's the problem, since I think I've seen
problems here even with GNU make.
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