pgsql: Add server authentication over Unix-domain sockets This adds a

Log Message:
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Add server authentication over Unix-domain sockets

This adds a libpq connection parameter requirepeer that specifies the user
name that the server process is expected to run under.

reviewed by KaiGai Kohei

Modified Files:
--------------
    pgsql/doc/src/sgml:
        libpq.sgml (r1.314 -> r1.315)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml?r1=1.314&r2=1.315)
    pgsql/src/interfaces/libpq:
        fe-connect.c (r1.398 -> r1.399)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-connect.c?r1=1.398&r2=1.399)
        libpq-int.h (r1.153 -> r1.154)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h?r1=1.153&r2=1.154)