Added tests for wmbc_mergewmb and corrected expansion bug

Signed-off-by: Mike Gerwitz <mike@mikegerwitz.com>
Removed length check from MakeWinMsgEv

The only remaining check (since now the buffer is dynamically expandable) is
for a seemingly arbitrary length. This removes the need for the `l'
variable; another variable gone.

Signed-off-by: Mike Gerwitz <mike@mikegerwitz.com>
Added WINESC_WIN_NUM

Signed-off-by: Mike Gerwitz <mike@mikegerwitz.com>
Removed fallthrough to %n for unknown winmsg escapes

I'm not sure why this was originally the case, but it does not make sense to
me that any undefined escape should implicitly mean %n; instead, any
undefined escapes will do nothing and output nothing (and consequently not
set the condition flag).

(It looks like the fallthrough may have been added in 80a04457 as part of a
larger commit, so the rationale isn't necessarily clear; I do not much feel
like researching it at this point, so I will discus it with amade.)

Signed-off-by: Mike Gerwitz <mike@mikegerwitz.com>
%n refactored into WinNum handler; all escapes now have handlers

Signed-off-by: Mike Gerwitz <mike@mikegerwitz.com>