Print shorter position without '-' character.
Reset numCharsDeleted when edit start is reset.

"Unallowed" movements (see line 406) will reset the current edit
register, but it wouldn't reset the numCharsDeleted field which would
keep growing. The result was that the updated "editing range" would span
from a negative offset to the current offset, setting off alarm bells in
Eclipse.

The field also used to be static, compounding the problem as several
editors in Insert mode could keep pushing the editing start position to
negative infinity.

Extend the createRepetition function to later support the DELETE key.

Fixes #553.
Log negative editing range start

Under certain circumstances the editing range start can still use a
negative offset (so far only observed when deleting everything in a file
using a mouse selection when visualmouse if off).

Log such an error to know how frequently it occurs.