reported by Markus Mauhart <qwe123@chello.at>. One was a simple typo; to
fix the other we call patsubst_expand() for all instances of variable
substitution, even when there is no '%'. We used to call subst_expand()
with a special flag set in the latter case, but it didn't work properly
in all situations. Easier to just use patsubst_expand() since that's
what it is.
GNU make. Also he provides some other performance fixups after doing
some profiling of make on large makefiles.
Modify the test suite to allow the use of Valgrind to find memory problems.
