Change to selection movement with virtual space

[Neil Hodgson]

When using multi-typing with two carets in virtual space on one line, the space was collapsed for the first caret so the typing did not go where intended. This has been fixed by converting virtual space to real character offsets in the generic code that handles moving the selection for insertions of text in the document.

This may cause changes in the behaviour of other features.

http://sourceforge.net/p/scintilla/code/ci/a0ed65c5aadf62c99e543b540a0c2556217b5367/

Neil