Reload file using most probable charset when it changes on disk

Previously if the file had been loaded as ASCII/UTF-8 and was changed on disk to something other than UTF-8, TextMate would go into infinite loop (retrying with UTF-8). It now uses the encoding classifier to find the most probable encoding (based on learned frequencies) falling back on ISO-8859-1, if there is no candidate.

Ideally it would bring up a warning, informing the user of the problem and allowing a manual correction of character set.

Fixes #1073.
Always place bookmarks on top of “search marks”

Logically I think the less temporary marks should be eclipsed, but this currently lead to inconsistencies with respect to hover images, e.g. hovering a search mark that also has a bookmark should show “remove bookmark” which it presently doesn’t, and will require a bit of refactoring to allow.

Issue #1132