lib: namedptr: thread-safe reference counted named object store

NamedPtr provides reference-counted handles to named objects.  The object
is created the first time the associated name is used, and stored under
the associated name until the last handle is destroyed.  NamedPtr may
itself be destroyed while handles are still active.

This template is intended to replace ResourceHandle with a more general
and less invasive implementation.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

test/Makefile

@@ -3,6 +3,7 @@ PROGRAMS = \
 	crc64 \
 	fd \
 	limits \
+	namedptr \
 	path \
 	process \
 	progress \