pgsql: Add PQprepare/PQsendPrepared functions to libpq to support

Log Message:
-----------
Add PQprepare/PQsendPrepared functions to libpq to support preparing
statements without necessarily specifying the datatypes of their parameters.
Abhijit Menon-Sen with some help from Tom Lane.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        libpq.sgml (r1.165 -> r1.166)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml.diff?r1=1.165&r2=1.166)
    pgsql/src/interfaces/libpq:
        exports.txt (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/exports.txt.diff?r1=1.1&r2=1.2)
        fe-exec.c (r1.163 -> r1.164)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-exec.c.diff?r1=1.163&r2=1.164)
        fe-protocol3.c (r1.18 -> r1.19)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-protocol3.c.diff?r1=1.18&r2=1.19)
        libpq-fe.h (r1.111 -> r1.112)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-fe.h.diff?r1=1.111&r2=1.112)
        libpq-int.h (r1.94 -> r1.95)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h.diff?r1=1.94&r2=1.95)