pgsql: Expose quote_literal_cstr() from core.

Expose quote_literal_cstr() from core.

This eliminates the need for inefficient implementions of this
functionality in both contrib/dblink and contrib/tablefunc, so remove
them. The upcoming patch implementing an in-core format() function
will also require this functionality.

In passing, add some regression tests.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=4343c0e546b216ab38a3397a4f0f7476d557b352

Modified Files
--------------
contrib/dblink/dblink.c | 20 ---------
contrib/tablefunc/tablefunc.c | 20 ---------
src/backend/utils/adt/quote.c | 75 +++++++++++++++++++++++++----------
src/include/utils/builtins.h | 1 +
src/test/regress/expected/text.out | 18 +++++++++
src/test/regress/sql/text.sql | 3 +
6 files changed, 75 insertions(+), 62 deletions(-)