pgsql: Add comment for deadlock_timeout: /* This is PGC_SIGHUP

Log Message:
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Add comment for deadlock_timeout:

/* This is PGC_SIGHUP so all backends have the same value. */

Modified Files:
--------------
pgsql/src/backend/utils/misc:
guc.c (r1.462 -> r1.463)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.462&r2=1.463)