Drop snippets on undo

This isn’t ideal but better than a potential crash (following the next edit). A better solution will have to wait to a larger refactoring (which should also consider multiple editors working on the same buffer).

Closes #186.
Revert "Do not timestamp our code signing"

Some users have reported issues opening TextMate: Finder tells them the program is corrupt and should be moved to trash. If the user adds his own (ah hoc) signature, then no such dialog is shown.

This reverts commit 1c164e3ce02465fd197463c0a72dfd804dd4b83e.
Proper refresh when dropping files on text view
Set “C pointer preference”

TextMate’s coding style is to have the asterisk bind to the type rather than the variable.
View → Show Invisibles now work for file browser

With focus in the file browser this menu item can now be used to toggle wether or not the include/exclude patterns should be ignored (causing everything to be shown, when ignored).
Fix typo: ammend → amend