Removed MPCG3 solver declaration in invert_quda.h.
This was only needed for testing purposes.
Have SimpleBiCGstab solver working. Note that this solver will only
be used to test Communication-avoiding BiCGstab.
Added a prototype matrix-powers bicgstab routine, which is still buggy.
Modified SimpleBiCGstab so that updates to r and p do not use the
intermediate vector s. This is less efficient than the formulation
that uses s, but will be used for debugging purposes.
MPBiCGstab seems to be working.
Fixed up stopping criterion in MPBiCGstab.