pgsql: Prefer pg_any_to_server/pg_server_to_any over pg_do_encoding_con

Prefer pg_any_to_server/pg_server_to_any over pg_do_encoding_conversion.

A large majority of the callers of pg_do_encoding_conversion were
specifying the database encoding as either source or target of the
conversion, meaning that we can use the less general functions
pg_any_to_server/pg_server_to_any instead.

The main advantage of using the latter functions is that they can make use
of a cached conversion-function lookup in the common case that the other
encoding is the current client_encoding.  It's notationally cleaner too in
most cases, not least because of the historical artifact that the latter
functions use "char *" rather than "unsigned char *" in their APIs.

Note that pg_any_to_server will apply an encoding verification step in
some cases where pg_do_encoding_conversion would have just done nothing.
This seems to me to be a good idea at most of these call sites, though
it partially negates the performance benefit.

Per discussion of bug #9210.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/769065c1b2471f484bb48bb58a8bdcf1d12a419c

Modified Files
--------------
contrib/pg_stat_statements/pg_stat_statements.c |    8 +++----
contrib/sslinfo/sslinfo.c                       |   10 ++-------
src/backend/commands/extension.c                |    8 ++-----
src/backend/snowball/dict_snowball.c            |   10 ++-------
src/backend/tsearch/ts_locale.c                 |    5 +----
src/backend/utils/adt/pg_locale.c               |   23 ++++++++-----------
src/backend/utils/adt/xml.c                     |   27 ++++++++---------------
src/backend/utils/mb/mbutils.c                  |    4 +++-
src/pl/plperl/plperl.c                          |    8 ++-----
src/pl/plperl/plperl_helpers.h                  |   25 ++++++---------------
src/pl/plpython/plpy_util.c                     |   15 +++++--------
src/pl/tcl/pltcl.c                              |    8 +++++--
12 files changed, 51 insertions(+), 100 deletions(-)