Handle tone-cancellation key 'z'.  Make Backspce delete the previous character instead of undoing.  Another fix for double vowel.
Handle tone-cancellation key 'z'.  Make Backspce
delete the previous character instead of undoing.  Another fix for
double vowel.

xmirror/m17n-db,xmirror/m17n-db,sanskrit-coders/m17n-db,sanskrit-coders/m17n-db,xmirror/m17n-db,xmirror/m17n-db,sanskrit-coders/m17n-db