Add new entries to lib/confmgt ".may_include" file

confparse.[ch] will need these; checkIncludes confirms that we have
not introduced a cycle.

src/lib/confmgt/.may_include

@@ -7,3 +7,5 @@ lib/encoding/*.h
 lib/log/*.h
 lib/malloc/*.h
 lib/string/*.h
+lib/testsupport/*.h
+ext/*.h