pgsql: When we are in error recursion trouble, arrange to suppress

Log Message:
-----------
When we are in error recursion trouble, arrange to suppress translation and
encoding conversion of any elog/ereport message being sent to the frontend.
This generalizes a patch that I put in last October, which suppressed
translation of only specific messages known to be associated with recursive
can't-translate-the-message behavior. As shown in bug #4680, we need a more
general answer in order to have some hope of coping with broken encoding
conversion setups. This approach seems a good deal less klugy anyway.

Patch in all supported branches.

Modified Files:
--------------
pgsql/src/backend/libpq:
pqformat.c (r1.48 -> r1.49)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/pqformat.c?r1=1.48&r2=1.49)
pgsql/src/backend/utils/error:
elog.c (r1.212 -> r1.213)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/error/elog.c?r1=1.212&r2=1.213)
pgsql/src/backend/utils/mb:
wchar.c (r1.71 -> r1.72)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mb/wchar.c?r1=1.71&r2=1.72)
pgsql/src/include/libpq:
pqformat.h (r1.27 -> r1.28)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/pqformat.h?r1=1.27&r2=1.28)