[GRASS5] d.erase: now also erases frame(s) with -f

[Markus Neteler]

Hi,

for (my personal) convenience I have added a -f flag
to d.erase for frames removal (such as done by d.rast.leg).

d.erase: erases as before
d.erase -f: does now the same as d.frame -e

So one has to teach only a single module instead of two.

Markus