Add low-level method to navigate to next character occurrence in current line

[jrk]

Vim's f & t commands are quite useful for fast navigation (and editing/deletion/correction, when combined with d or c). Emulating this functionality seems to require an additional low-level Objective-C method injected into TextMate which can emulate the f and t navigation scheme with and without changing the selection, and without leaving the current line (all unlike the existing ISIM_incrementalSearch method).

The old incremental search InputManager code is a useful reference.