pgsql: Remove support for (insecure) crypt authentication.

Log Message:
-----------
Remove support for (insecure) crypt authentication.

This breaks compatibility with pre-7.2 versions.

Modified Files:
--------------
pgsql/doc/src/sgml:
client-auth.sgml (r1.109 -> r1.110)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/client-auth.sgml?r1=1.109&r2=1.110)
protocol.sgml (r1.73 -> r1.74)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/protocol.sgml?r1=1.73&r2=1.74)
user-manag.sgml (r1.40 -> r1.41)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/user-manag.sgml?r1=1.40&r2=1.41)
pgsql/src/backend/libpq:
auth.c (r1.169 -> r1.170)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/auth.c?r1=1.169&r2=1.170)
crypt.c (r1.75 -> r1.76)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/crypt.c?r1=1.75&r2=1.76)
hba.c (r1.171 -> r1.172)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/hba.c?r1=1.171&r2=1.172)
pgsql/src/backend/postmaster:
postmaster.c (r1.565 -> r1.566)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/postmaster.c?r1=1.565&r2=1.566)
pgsql/src/include/libpq:
hba.h (r1.50 -> r1.51)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/hba.h?r1=1.50&r2=1.51)
libpq-be.h (r1.67 -> r1.68)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/libpq-be.h?r1=1.67&r2=1.68)
pqcomm.h (r1.108 -> r1.109)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/pqcomm.h?r1=1.108&r2=1.109)
pgsql/src/interfaces/libpq:
fe-auth.c (r1.137 -> r1.138)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-auth.c?r1=1.137&r2=1.138)
fe-connect.c (r1.364 -> r1.365)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-connect.c?r1=1.364&r2=1.365)
libpq-int.h (r1.135 -> r1.136)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h?r1=1.135&r2=1.136)