Improve getObjectDescription's display of pg_amop and pg_amproc entries.

Improve getObjectDescription's display of pg_amop and pg_amproc entries.

Include the lefttype/righttype columns explicitly (instead of assuming
the reader can deduce them from the operator or function description),
and move the operator or function description to the end of the string,
to make it clearer that it's a referenced object and not the amop or
amproc item itself.  Per extensive discussion of Andreas Karlsson's
original patch.

Andreas Karlsson, Tom Lane