Implemented fast weighted alignment with align!=displace

In this version the fast routine is hard-coded. I do not compute explicitly the derivatives of the rotational matrix.
Instead, I assume them to be zero and at the end add a contribution which resets total "force" and "torque" (i.e.
I enforce translational and rotational invariance of the RMSD). In test rt47/check one can appreciate that
numerical derivatives come out correct. I do not know exactly why...
Added internal lapack/blas

Adapted from GROMACS
missing regtest
libmolfile plugin in driver
test for molfile_plugin
added rt2
Missing malloc. Thanks to Toni
Merge branch 'v2.0' into internal-lapack
Merge branch 'v2.0' into internal-lapack
Fixed configuration file)
(suggested by Toni Giorgino)
Merge branch 'v2.0' into internal-lapack
Added MPI based implementation of multiple walkers

It is still preliminary and not very well optimized.
It only works with MPI (i.e. all processes should be part of the same
MPI job). In the future we might think to allow groups of MPI walkers
exchanging information through the filesystems.

Addresses issue plumed/plumed2#12
Added regtest for WALKERS_MPI
Merge branch 'master' into walkers-mpi
Merge branch 'master' into walkers-mpi
Fixed automatic backbone detection for secondary structure variables

The nature of the backbone is now specified by a class called MolDataClass.
A warning is given about GLY residues
Added functionality to read torsions for proteins using psi-4 or phi-6
Merge branch 'master' into walkers-mpi
Improved RMSD with align!=displace

I did it in the boring way - full derivatives of rotation matrix.
It seems to work now, but still breaks some test. It is probably
some numerical issue, I will investigate before merging.

It is slower than the align==displace version (~ a factor 1.5),
but I think it is more than acceptable.
Merge branch 'v2.0' into fast-weighted-msd-derivs

(also moved rt47)

Conflicts:
	src/tools/RMSD.cpp