r.mdig.survival uses r.mask, the use of r.mask to set the treatment area will not work

[ferrouswheel]

Discovered a major bug in management working with r.mdig.survival.

Since r.mdig.survival uses r.mask, the use of r.mask to set the treatment area will not work!

Have committed a fix, but it is untested. I really need to come up with a series of test scenarios for r.mdig.survival because the script is getting complex! Possible tests:

• with and without seed value. Test would ensure that a certain seed always produced the same result... this would be great for testing everything actually!
• ensure that survival 0 means nothing is shown
• survival 100+ means everything survives

[ferrouswheel]

Replaced by #16 - r.mdig.survival behaves correctly, but it could still do with more tests.