Previously word drag and shift selection was not implemented.  Line
drag selection was working, but shift selection wasn't.

The error was a memory access of a freed object.  In ME_AddUndoItem I
checked the top of the undo stack to end a coalescing undo transaction,
assuming that this should be either a valid undo item, or NULL, instead
it was already freed.

Constant numbers start at 0, and the loading loop has a for(i; i <
dirtyconsts; i++). This means that the highest dirty constant isn't
loaded correctly. Rather than replacing the < with <=, which would
make it impossible to have no dirty constant, add 1 to the dirty
constant counter.