Fixes mimicgeom / total mass issue with kinbody reader.

The current version of the Kinbody XML reader assumes that when
"mimicgeom" is specified as the mass type, the user has specified
density (not total mass).  Setting a total mass has no effect because
the fTotalMass property is not read in this mode. The fix follows 4
steps:

1.  Calculate each geom's mass assuming a dummy density (1000kg/m^3)
2.  Add all geom masses to find a total dummy mass
3.  Scale each geom's mass by the ratio of the assigned mass over the dummy mass.
4.  Sum and store the totalmass property.

It would likely be more elegant or simple to work directly with volume,
but this method was quick and easy.
Merge pull request #235 from robEllenberg/feature/totalmass

Fixes mimicgeom / total mass issue with kinbody reader.
ikfast polyroots now handles case when leading coeff is 0
better free increment values