This was a workaround to be able to build on case-insensitive file
systems where it might get confused about <string.h> vs <String.h>.
Let's just not support building that way, so String.h can have an
objectively nicer name. :^)
We were checking the columns of the whole selection instead of the
the specfic line were modifying. Because of this, the selection
remained if the selection's column on another line was less than
the cursor.
