Update libpq to make new features of FE/BE protocol available to

doc/src/sgml/libpq.sgml

doc/src/sgml/lobj.sgml

src/interfaces/libpq/blibpqdll.def

src/interfaces/libpq/fe-connect.c

src/interfaces/libpq/fe-exec.c

src/interfaces/libpq/fe-misc.c

src/interfaces/libpq/fe-protocol2.c

src/interfaces/libpq/fe-protocol3.c

src/interfaces/libpq/libpq-fe.h

src/interfaces/libpq/libpq-int.h

src/interfaces/libpq/libpqdll.def