This avoids additional translatable strings for each distinct type, as
well as making our quoting style around type names more consistent
(namely, that we don't quote type names). This continues what started
as f402b9950120.
Discussion: https://postgr.es/m/20160401170642.GA57509@alvherre.pgsql
The plain C string language name needs to be wrapped in makeString() so
that the parse tree is copyable. This is detectable by
-DCOPY_PARSE_PLAN_TREES. Add a test case for the COMMENT case.
Also make the quoting in the error messages more consistent.
discovered by Tom Lane
This provides a mechanism for specifying conversions between SQL data
types and procedural languages. As examples, there are transforms
for hstore and ltree for PL/Perl and PL/Python.
reviews by Pavel Stěhule and Andres Freund
