Log Message:
Changes 8.1.17:
* Prevent error recursion crashes when encoding conversion fails.
* Disallow "CREATE CONVERSION" with the wrong encodings for the
  specified conversion function.
* Fix core dump when to_char() is given format codes that are
  inappropriate for the type of the data argument.
* Fix decompilation of CASE WHEN with an implicit coercion.
* Fix possible misassignment of the owner of a TOAST table's rowtype.
* Clean up PL/pgSQL error status variables fully at block exit.
* Add MUST (Mauritius Island Summer Time) to the default list of
  known timezone abbreviations.