MODIFIED: Handling of pengine source isolation and reclaiming of resources
is now based on the new temporary module support of SWI-Prolog instead of
the support for thread local predicates.  This provides better isolation,
and will allow for features such as defining operators and managing the
location of sources.
Typos
Fixed singleton in test
MODIFIED: Process src_text and src_url using the new temporary modules.
MODIFIED translate the `src_predicates` and `src_list` options to
`src_text`, so we can uniformly handle all Prolog source on the server
side.
Fixed source options for pengine_rpc/2,3
SECURITY: Use version 4 UUIDs.  The default version 1 UUIDs are predictable.