[Bf-codereview] Multi-byte (utf8) text field editing (issue 5285050)

[ideasman42 at gmail.com]

Reviewers: bf-codereview_blender.org,

Message:
Patch so you edit partial characters when editing text fields.

Description:
This patch makes moving the cursor about, backspace, delete etc, work
for multi-byte characters (utf8)

Please review this at http://codereview.appspot.com/5285050/

Affected files:
   M     source/blender/blenlib/BLI_string.h
   M     source/blender/blenlib/intern/string_utf8.c
   M     source/blender/editors/interface/interface_handlers.c