lift limits on handle allocation and reuse (#95)

The old entity handle mechanism suffered from a number of problems, the
most terrible one being that it would only ever allocate 1000 handles
(not even have at most 1000 in use at the same time).  Secondarily, it
was protected by a single mutex that actually does show up as a limiting
factor in, say, a polling-based throughput test with small messages.
Thirdly, it tried to provide for various use cases that don't exist in
practice but add complexity and overhead.

This commit totally rewrites the mechanism, by replacing the old array
with a hash table and allowing a near-arbitrary number of handles as
well as reuse of handles.  It also removes the entity "kind" bits in the
most significant bits of the handles, because they only resulted in
incorrect checking of argument validity.  All that is taken out, but
there is still more cleaning up to be done.  It furthermore removes an
indirection in the handle-to-entity lookup by embedding the
"dds_handle_link" structure in the entity.

Handle allocation is randomized to avoid the have a high probability of
quickly finding an available handle (the total number of handles is
limited to a number much smaller than the domain from which they are
allocated).  The likelihood of handle reuse is still dependent on the
number of allocated handles -- the fewer handles there are, the longer
the expected time to reuse.  Non-randomized handles would give a few
guarantees more, though.

It moreover moves the code from the "util" to the "core/ddsc" component,
because it really is only used for entities, and besides the new
implementation relies on the deferred freeing (a.k.a. garbage collection
mechanism) implemented in the core.

The actual handle management has two variants, selectable with a macro:
the preferred embodiment uses a concurrent hash table, the actually used
one performs all operations inside a single mutex and uses a
non-concurrent version of the hash table.  The reason the
less-predeferred embodiment is used is that the concurrent version
requires the freeing of entity objects to be deferred (much like the
GUID-to-entity hash tables in DDSI function, or indeed the key value to
instance handle mapping).  That is a fair bit of work, and the
non-concurrent version is a reasonable intermediate step.

Signed-off-by: Erik Boasson <eb@ilities.com>

src/tools/pubsub/common.c

@@ -390,7 +390,6 @@ static void inapplicable_qos(dds_entity_kind_t qt, const char *n) {
     case DDS_KIND_COND_READ: en = "cond read"; break;
     case DDS_KIND_COND_QUERY: en = "cond query"; break;
     case DDS_KIND_WAITSET: en = "waitset"; break;
-    case DDS_KIND_INTERNAL: en = "internal"; break;
     default: en = "?"; break;
     }
     fprintf(stderr, "warning: %s entity ignoring inapplicable QoS \"%s\"\n", en, n);