tools in the tools menu need to be able to manipulate code as a single
edit, rather than a delete followed by a replace which is how it's
happening now. this affects how undo works because the first undo after
using a tool will cause the code to go blank.

because of bug #110, this becomes especially important. when
auto format mangles code, undo will make the code disappear. a second undo
will bring things back but more likely people will just freak out.

fixed for 0098.