[rancid] Disabling timestamp on Cisco IO devices

[Per Carlson]

Hi.

We have enabled timestamping of all "show commands" on those Cisco IOS
devices supporting it. The actual configuration looks like:

line vty <form> <to>
exec prompt timestamp

When doing for example "show version", the output is prepended by a
CPU load indicator as well as a timestamp:

router>show version
Load for five secs: 0%/0%; one minute: 0%; five minutes: 0%
Time source is NTP, 09:57:49.061 CET Tue Nov 17 2009
Cisco Internetwork Operating System Software
IOS (tm) GS Software (C12KPRP-K4P-M), Version 12.0(33)S5, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2009 by cisco Systems, Inc.
<snip/>

The timestamp will of course differ at each run, which makes RANCID
detect a diff on each and every "show command". Not good.

The solution to the problem is disabling the timestamping (by the
command "terminal no exec prompt timestamp") before running the "show
commands". My approach to this is adding a command to the top of the
commandtable list, and expanding the DoNothing sub slightly. The patch
is attached.