[test] Switch to automake-based test-runner

Adds check-valgrind among other modes.  We do not run under gtester by
default anymore.
diff --git a/Makefile.am b/Makefile.am
index 446c18a..12a42e6 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,3 +1,5 @@
+# Process this file with automake to produce Makefile.in
+
 NULL =
 
 SUBDIRS = src test