! A couple more changes for IE11

This adds support for detecting IE11 (based on both Gecko and Trident being in the user agent, which seems to be the best method for now) and also fixes the "listen to the letters" feature in IE11.

Note that IE11 is currently singled out - isBrowser('is_ie') will return false for IE11. SMF uses isBrowser('is_ie') in three spots, and only one of those situations applies to IE11 as well (at least from what I can tell). Easier to modify one line of code for IE11 support than to modify two lines of code to exclude IE11 :wink:

Signed-off-by: Michael Eshom <oldiesmann@oldiesmann.us>