Don't clobber global 'updatetime' setting

Commit ff72bd9b added input debouncing, and along with it a bug in which
we were setting the global 'updatetime' setting and not restoring it.

The default value of 50 could make some mappings such as <C-X>_<C-P>
unlikely to work after opening Command-T.

This commit saves and restores the setting on opening/closing the match
window. I applied some local clean-up as well, making the controller's
`#get_number` method accept a default argument.

Thanks to Michael Jansen for the bug report.

Signed-off-by: Wincent Colaiuta <win@wincent.com>