Modified rtksubselect :
It can now take in input a single file containing several projections.
It now writes its output projections in a single file too.
Merge https://github.com/SimonRit/RTK
Merge https://github.com/SimonRit/RTK
Moved the check on the type of forward / back projector (the one
that determines whether or not the filter should be Modified() )
from SART, ConjugateGradient and ADMMTV to the mother class
IterativeConeBeamReconstructionFilter.
Merge https://github.com/SimonRit/RTK

Conflicts:
	applications/rtkconjugategradient/rtkconjugategradient.cxx
Removed a useless include. RTK should now compile with ITK 4.1.0
and newer versions.
Merge https://github.com/SimonRit/RTK