Some of our rules used $(PERL), while others used 'perl'. Always
using the variable allows a developer to point to a different (often
better) perl than the default one found on $PATH.
* daemon/Makefile.am ($(srcdir)/remote_dispatch.h): s/perl/$(PERL).
* src/Makefile.am ($(srcdir)/remote/remote_client_bodies.h)
(PDWTAGS, %protocol.c, %_probes.stp): Likewise.