ADDED: library(sandbox): declare term_hash/2,3 and variant_sha1/2 as safe.
Ensure dict{braces} emit a token, even when using specified colouring
for the tag and keys.
Updated pldoc
Fixed prolog_colourise_query/3 for syntax error handling.
FIXED: https://github.com/SWI-Prolog/swipl-devel/issues/17: GC crash on
optimized unification.
FIXED:  Also use skippedVar() for optimized == and \==.