Empty make check on ultrix 4.5

[Kevin Ryde]

I had the misfortune to try automake 1.5 on vax-dec-ultrix4.5.  If a
TESTS list is empty, due to conditionals perhaps, a "make check" will
fail.  Apparently /bin/sh on that system gives a non-zero exit for
something like

        if test -n ""; then blah blah; fi

The below would add an "else true;" to avoid that situation

        * lib/am/check.am (check-TESTS): Add an "else true" to work with
        Ultrix 4.5 /bin/sh when $(TESTS) is empty.

check.am.elsetrue.diff
Description: Source code patch