bug#13839: xterm/mintty control sequences support when formatOtherKeys = 1

[Stefan Monnier]

>> Can you confirm that the patch below works for your formatOtherKeys=1 case?
> There is no problem in the patch itself.

Thanks, installed.

> But the xterm extra capability support
> does not work automatically due to another bug in lisp/term/xterm.el -
> the regexp in line 532 ">0;\\([0-9]+\\);0".  It should be
> ">[0-9]+;\\([0-9]+\\);0".

Hmm...

> The default value is 41 (in xterm latest version manual).

It seems that indeed the regexp could need revision, but I'd first like
to understand what's going on.  The test we want to make is "make sure
this terminal understands this and that feature".  So the "P v" field
(the version number) only makes sense if the terminal is actually an
xterm (or uses a version numbering that implies the same featureset).
In my xterms the "P p" value is always 0 and not 41 as you seem to suggest.

More specifically, I'm concerned that by accepting any "P p" number, we
might end up trying to use a feature that's not supported by the
underlying terminal emulator because it happens to have version numbers
that are higher than those of "the usual xterm".


        Stefan