Fix operator support functions Operators used in an operator class should not be based on SQL functions, which might be inlined, thus preventing index usage based on the operator. Schema qualify functions called inside functions to make the outer function work independendly from search_path setting. This makes it possible to use the operators using the 'OPERATOR(<schema>.<opname>)' syntax. Most importantly, it fixes the usage of isrs_diff() during autovacuum.

teichmann@intevation.de = sascha.teichmann@intevation.de
bernhard.reiter@intevation.de = bernhard@intevation.de