pgsql: SSPI authentication on Windows.

Log Message:
-----------
SSPI authentication on Windows. GSSAPI compatible client when doing Kerberos
against a Unix server, and Windows-specific server-side authentication
using SSPI "negotiate" method (Kerberos or NTLM).

Only builds properly with MSVC for now.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        client-auth.sgml (r1.99 -> r1.100)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/client-auth.sgml.diff?r1=1.99&r2=1.100)
        libpq.sgml (r1.238 -> r1.239)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml.diff?r1=1.238&r2=1.239)
    pgsql/src/backend/libpq:
        auth.c (r1.153 -> r1.154)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/auth.c.diff?r1=1.153&r2=1.154)
        hba.c (r1.161 -> r1.162)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/hba.c.diff?r1=1.161&r2=1.162)
        pg_hba.conf.sample (r1.63 -> r1.64)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/pg_hba.conf.sample.diff?r1=1.63&r2=1.64)
        pqcomm.c (r1.193 -> r1.194)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/pqcomm.c.diff?r1=1.193&r2=1.194)
    pgsql/src/backend/postmaster:
        postmaster.c (r1.533 -> r1.534)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/postmaster.c.diff?r1=1.533&r2=1.534)
    pgsql/src/include/libpq:
        hba.h (r1.46 -> r1.47)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/hba.h.diff?r1=1.46&r2=1.47)
        libpq-be.h (r1.61 -> r1.62)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/libpq-be.h.diff?r1=1.61&r2=1.62)
        pqcomm.h (r1.105 -> r1.106)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/pqcomm.h.diff?r1=1.105&r2=1.106)
    pgsql/src/interfaces/libpq:
        fe-auth.c (r1.127 -> r1.128)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-auth.c.diff?r1=1.127&r2=1.128)
        fe-connect.c (r1.349 -> r1.350)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-connect.c.diff?r1=1.349&r2=1.350)
        libpq-int.h (r1.123 -> r1.124)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h.diff?r1=1.123&r2=1.124)
    pgsql/src/tools/msvc:
        Mkvcbuild.pm (r1.14 -> r1.15)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Mkvcbuild.pm.diff?r1=1.14&r2=1.15)
        Solution.pm (r1.29 -> r1.30)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Solution.pm.diff?r1=1.29&r2=1.30)