Intercept part input change event.

In some cases (when 'Close editors automatically' is enabled for ex.)
Eclipse can substitute the underlying editor of an already opened part.
Handle this case by resetting the references associated with the part.
Keep cursor near selection end on visual mode exit

Vim will keep the cursor in the very same spot when exiting visual mode
whereas Vrapper would always reset the selection to the top- and
left-most point of the selection.

Try to reset the pointer to a point nearest the end of the selection,
accounting for reverse selections.

Note that this isn't 100% visually correct for visual line-wise mode.
Vim draws a caret inside the selection, whereas Eclipse can only draw
the caret at the end of the selection. Since we now jump to the
position within the selection (as Vim would do), the user might be
slightly surprised to see his caret move. A hack to show the caret in
the "right" position might be added later.

Fixes #391.
placeCursor() called correctly in enterMode call

The call to placeCursor() was a no-op because it only works if
super.enterMode(..) gets called before it.

This fix is to get proper cursor placement after leaving visual mode.
Merge pull request #401 from igrekster/part-input-changed

Intercept part input change event.
Update unstable update site.
Fix position of caret for textoperations.

TextOperationCommand tends to reset the selection already, making the
-1/+1 trick run into a one-off situation.

Only move the pointer if we're actually executing LeaveVisualCommand,
not just in the doIt method.