pbx.c: Print new context count when reloading dialplan.

pbx.c: Print new context count when reloading dialplan.

When running "dialplan reload", the number of contexts reported
is initially wrong, as it is the old context count. Running
"dialplan reload" a second time returns the correct number of
contexts that are loaded. This can confuse users into thinking
that the reload didn't work successfully the first time.

This counter is currently only incremented when iterating the
old contexts prior to the context merge; at the very end, get
the current number of elements in the context hash table and
report that instead. This way, the count is correct immediately
whenever a reload occurs.

Resolves: #1599