Adding in Axel's special math functions that give about 2% speed-up on the rhodo problem.

git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@9311 f3b2605a-c512-4ea7-a41b-209d697bcdaa
Merge branch 'master' into lammps-icms
Merge branch 'lammps-icms' of git://git.icms.temple.edu/lammps-icms into lammps-ictp
fix typo in comment
simplify the powsinxx(x,n) code and add cube() and powint(x,n).