pgsql: Code review for log_lock_waits patch.

Log Message:
-----------
Code review for log_lock_waits patch. Don't try to issue log messages from
within a signal handler (this might be safe given the relatively narrow code
range in which the interrupt is enabled, but it seems awfully risky); do issue
more informative log messages that tell what is being waited for and the exact
length of the wait; minor other code cleanup. Greg Stark and Tom Lane

Modified Files:
--------------
pgsql/doc/src/sgml:
config.sgml (r1.126 -> r1.127)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml.diff?r1=1.126&r2=1.127)
pgsql/src/backend/storage/lmgr:
deadlock.c (r1.47 -> r1.48)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/deadlock.c.diff?r1=1.47&r2=1.48)
lmgr.c (r1.90 -> r1.91)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/lmgr.c.diff?r1=1.90&r2=1.91)
proc.c (r1.188 -> r1.189)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/proc.c.diff?r1=1.188&r2=1.189)
pgsql/src/backend/utils/misc:
guc.c (r1.398 -> r1.399)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.398&r2=1.399)
pgsql/src/include/storage:
lmgr.h (r1.57 -> r1.58)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/lmgr.h.diff?r1=1.57&r2=1.58)
lock.h (r1.105 -> r1.106)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/lock.h.diff?r1=1.105&r2=1.106)