#459 editor: backspace/left arrow trim spaces in curr line

[Marek Januszewski]

when trim trailing spaces is on - pressing couple of
spaces or tabs and then left arrow or backspace moves
to column one trimming all the previously typed
spaces/tabs. expected behaviour would be to delete/move
to previous character (space or tab)

[Marek Januszewski]

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submitted to synedit:

http://sourceforge.net/tracker/index.php?func=detail&aid=1077209&group_id=3221&atid=103221