Added two new bonded functions.

Added two new bonded functions.

The first one implements a potential for linear angles without any
discontinuities at 180 degrees. A paper is being written about this. The
potential has [ angles ] type 9 or F_LINEAR_ANGLES internally.
A free energy option has been implemented as well for the linear angles.
The second is an anharmonic polarization function, based on the normal harmonic
term plus a forth order term, as introduced by the Roux group in
J. Chem. Theor. Comput. 6 (2010) p. 774-786. The potential has [ polarization ]
type 2 or F_ANHARM_POL internally.

Change-Id: I0497ed20baf1c1c0b2a6c2354eed77bc9ed75c6d