[GRASS5] OVERWRITE

[Radim Blazek]

New GRASS users are usually surprised that most GRASS modules silently 
or with warning overwrite existing maps. Most normal users
however like this feature (AFAIK).

Some modules have -o (overwrite) option ( e.g. r.composite, g.copy ).
For vector maps it is possible to set OVERWRITE variable to 0
to disable overwriting but default (if not set) is 1 (overwrite).

My suggestion is:
1) use OVERWRITE GRASS variable also in G_open_cell_new,
    if OVERWRITE=0 and raster exists G_open_cell_new will call
    G_fatal_error (?, not sure)
2) change OVERWRITE default value to 0 (don't overwrite)
3) Add a new function G_force_overwrite which can force
    overwriting even if OVERWRITE=0. Modules with -o flag can use
    if ( flag_o->answer )
        G_force_overwrite();
    before calling G_open_cell_new


Radim