- returns index with MSK_CUT in upper nibble
- Cut is initiated with Ctrl-X or Shif-Delete
- Same as Get/Copy (F6/Ctrl-V) except the source item is removed

* Ctrl-Insert is now supported for Copy (in addition to Ctrl-C and F5)
* Shift-Insert is now supported for Paste (in addition to Ctrl-V and F6)

* Fixed a couple of potential NULL savbuf dereferences (one sighted when using
mouse).