Make rotation switchable on a per-particle level

When SWITCHABLE_ROTATION is defined in myconfig.h,
part ... rotation 1
activates rotation for a specific particle.
SWITCHABLE_ROTATION is incompatible with pressure calculation, as there is no method to count the number of degrees of freedom, yet.
SWITCHABLE_ROTATION: Added to feature list in config.c
Dipolar all with all - no replicas: Respect boundary conditions set by setmd
SWITCHABLE_ROTATION implies ROTATION.

Conflicts:

	communication.c
	config.h
Merge branch 'master' into switchable-rotation.

Conflicts:
	doc/ug/features.tex
	doc/ug/part.tex
	myconfig-sample.h
	src/communication.c
	src/config.c
	src/config.h
	src/magnetic_non_p3m_methods.c
	src/pressure.c
	src/pressure.h
in add_constraint_force, exit early if no constraints are active
The code from check_forces() which checks if a force is nan
into rescale_forces...() to avoid an additional iteration over all particles
Bugfix to thermostat: Fixed particles got thermostat forces
Merge branch 'master' into switchable_rotation2
Fixed ROTATION_PER_PARTICLE.
Merge branch 'master' into rotation_per_particle

Conflicts:
	NEWS
	src/magnetic_non_p3m_methods.c
	src/particle_data.c
	src/rotation.c
Merge branch 'master' into rotation_per_particle
Fixed regression in rotation_per_particle
Updated NEWS.
Merge branches 'olaf' and 'rotation_per_particle'

Conflicts:
	NEWS
	doc/ug/features.tex
	myconfig-sample.h.in
	src/config.h
	src/magnetic_non_p3m_methods.c
	src/particle_data.c
	src/rotation.c
	src/tcl/config_tcl.c
	src/tcl/particle_data_tcl.c
fixed set but unused variables

Conflicts:

	src/comforce.c
	src/debug.c
	src/p3m-dipolar.c
	src/tcl/statistics_tcl.c
doxy fixes
Merge remote-tracking branch 'trichter/3.1' into 3.1
Merge branch '3.1'
Merge branch 'master' of git://github.com/espressomd/espresso