XSB Src (SVN)-old

Back out previous fix, since gcc barfs on it. Have to find a fix that
works there too.

Fixed (I hope) an intermittent bug in hash_cons (intern) processing.

Fixed typo in an error message.

Fixed indexing and dynamic bugs in load_forest_log.

Changed itereated testsuite for SVN.

Add support for using .prolog as a source file extension. May not be complete.

Updated the multi-threading tests for the changes to the thread_sleep/1 predicate.

added flag_defs_xsb.h

made the dreaded Exiting XSB abnormally appear as a runtime error rather than a
feedback message

Fixed thread_sleep/1 to accept seconds as per draft standardization proposal. Changed handling of the at_exit/1 thread handler so that its success, failure, or error doesn't affect the thread exit status. Fixed bug in handling exceptions resulting from thread cancellation using a throw/1 signal.