Modifying general_purpose_block_preconditioner.h
to use the new concatenate_without_communication functions
Took out build_preconditioner_matrix, which is Richard's concatenation
function, from block_preconditioner.cc and .h
Modified ExactBlockPreconditioner from
general_purpose_block_preconditioners.h to use my concatenation function
This seemed to have caused some self tests to fail. I need to fix this.
Put in general_block_preconditioner.h in the lll script