pgsql: Add PQisthreadsafe() to libpq, to allow library applications to

Log Message:
-----------
Add PQisthreadsafe() to libpq, to allow library applications to query
the thread-safety status of the library.

Modified Files:
--------------
pgsql/doc/src/sgml:
libpq.sgml (r1.210 -> r1.211)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml.diff?r1=1.210&r2=1.211)
pgsql/src/interfaces/libpq:
exports.txt (r1.8 -> r1.9)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/exports.txt.diff?r1=1.8&r2=1.9)
fe-exec.c (r1.183 -> r1.184)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-exec.c.diff?r1=1.183&r2=1.184)
libpq-fe.h (r1.128 -> r1.129)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-fe.h.diff?r1=1.128&r2=1.129)