New options for GMCJDriver

[pochoarus]

New options:
-force the interaction.
-use logarithmic binning in pmax.
-change the safety factor.

[candreop]

This set of changes seems OK to me. Any comments @nusense ? Otherwise will merge sometime later this week.

[nusense]

let me try this again

[pochoarus]

i've modified the code in order to address robert's suggestion.

[nusense]

Github's diff engine makes this a bit confusing to review (it's not very smart about small additions, and it makes it look like big blocks of code are being deleted and then added). But I think this change addresses the issues I had concerns about.