pgsql: Specify lo_write() to take a _const_ buffer, to match

Log Message:
-----------
Specify lo_write() to take a _const_ buffer, to match documentation.

Modified Files:
--------------
    pgsql/src/backend/libpq:
        be-fsstubs.c (r1.82 -> r1.83)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/be-fsstubs.c.diff?r1=1.82&r2=1.83)
    pgsql/src/backend/storage/large_object:
        inv_api.c (r1.119 -> r1.120)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/large_object/inv_api.c.diff?r1=1.119&r2=1.120)
    pgsql/src/include/libpq:
        be-fsstubs.h (r1.26 -> r1.27)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/be-fsstubs.h.diff?r1=1.26&r2=1.27)
    pgsql/src/include/storage:
        large_object.h (r1.34 -> r1.35)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/large_object.h.diff?r1=1.34&r2=1.35)
    pgsql/src/interfaces/libpq:
        fe-lobj.c (r1.58 -> r1.59)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-lobj.c.diff?r1=1.58&r2=1.59)
        libpq-fe.h (r1.132 -> r1.133)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-fe.h.diff?r1=1.132&r2=1.133)