pgsql: Replace strncpy with strlcpy in selected places that seem

Log Message:
-----------
Replace strncpy with strlcpy in selected places that seem possibly relevant
to performance. (A wholesale effort to get rid of strncpy should be
undertaken sometime, but not during beta.) This commit also fixes dynahash.c
to correctly truncate overlength string keys for hashtables, so that its
callers don't have to anymore.

Modified Files:
--------------
pgsql/src/backend/commands:
prepare.c (r1.64 -> r1.65)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/prepare.c.diff?r1=1.64&r2=1.65)
pgsql/src/backend/nodes:
read.c (r1.48 -> r1.49)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/read.c.diff?r1=1.48&r2=1.49)
pgsql/src/backend/storage/ipc:
shmem.c (r1.95 -> r1.96)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/shmem.c.diff?r1=1.95&r2=1.96)
pgsql/src/backend/utils/error:
elog.c (r1.173 -> r1.174)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/error/elog.c.diff?r1=1.173&r2=1.174)
pgsql/src/backend/utils/fmgr:
dfmgr.c (r1.89 -> r1.90)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/fmgr/dfmgr.c.diff?r1=1.89&r2=1.90)
pgsql/src/backend/utils/hash:
dynahash.c (r1.71 -> r1.72)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/hash/dynahash.c.diff?r1=1.71&r2=1.72)
hashfn.c (r1.27 -> r1.28)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/hash/hashfn.c.diff?r1=1.27&r2=1.28)
pgsql/src/backend/utils/misc:
ps_status.c (r1.31 -> r1.32)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/ps_status.c.diff?r1=1.31&r2=1.32)
pgsql/src/backend/utils/mmgr:
portalmem.c (r1.94 -> r1.95)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mmgr/portalmem.c.diff?r1=1.94&r2=1.95)
pgsql/src/port:
path.c (r1.68 -> r1.69)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/port/path.c.diff?r1=1.68&r2=1.69)
thread.c (r1.34 -> r1.35)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/port/thread.c.diff?r1=1.34&r2=1.35)