(proced-signal-list): Add POSIX 1003.1-2001 signals.

(proced-signal-list): Add POSIX 1003.1-2001 signals.
(proced-mode-map): Add tooltips for menus.  Use radio buttons for
listing types.
(proced-log-buffer): New variable.
(proced-mark-all, proced-unmark-all, proced-do-mark-al): Operate
on region if transient-mark-mode is turned on and the region is
active.
(proced-omit-processes): Renamed from proced-hide-processes to
avoid key clash with describe-mode (bound to h).  Search for
marked processes starting from point-min.
(proced-header-space): Removed.
(proced-send-signal): Handle errors.  Operate on current process
if no process is marked.
(proced-why): New command.
(proced-log, proced-log-summary): New functions.
(proced-help): Use proced-why.