[rancid] '>' in default prompt causes problems for zrancid

[Tore Anderson]

After an upgrade from RANCID 2.3.2, zrancid is creating bogus diffs.
They always involve the character «e» appearing/disappearing at the
beginning of lines, like so:

-log file /var/log/quagga/zebra.log
+elog file /var/log/quagga/zebra.log

Or at the end of lines, like so:

- ipv6 nd suppress-ra
+ ipv6 nd suppress-rae

I've traced this to a change in the default prompt in clogin.in that
happened in RANCID 2.3.6. Fast forwarding to RANCID 3.0, the relevant
code is as follows (lines 766-770 of clogin.in):

    # Default prompt.
    set prompt [join [find prompt $router] ""]
    if { [llength $prompt] == 0 } {
	set prompt "(>|#| \\(enable\\))"
    }

In RANCID 2.3.5 and earlier, $prompt was set to "(#| \\(enable\\))" by
default, and that worked perfectly for me.

I haven't yet been able to fully understand why the ">" match is causing
problems, but I did notice that it causes $prompt_match to always be set
to ">" at lines 576-579 of clogin.in:

        -re "$prompt"           {
                                  set prompt_match $expect_out(0,string);
                                  break;
                                }

However, the routers in question don't use ">" in their prompt (they use
"#"), so I don't think this can be right.

Attempting to escape the ">" (using "\>" or "\\>") makes no difference.
Removing it or replacing it with any other character (including "<")
does help, though, and in this case $prompt_match gets set to "#" as
expected, and the spurious «e» characters stop appearing.

The platform is Ubuntu 12.04.4 with expect 5.45.

Tore