libdbm is broken in 4.2

[Peter Gross]

In Mark's fix to the libdbm Makefile, he omitted the ranlib of the
created archive.  Thus,

change
	libdbm.a: dbm.o
		ar rv libdbm.a dbm.o
to
	libdbm.a: dbm.o
		ar rv libdbm.a dbm.o
		ranlib libdbm.a

--peter