Add user mpi communicator feature.

compute/pzgetrf.c

compute/zgetrf.c

control/control.c

control/descriptor_ipiv.c

coreblas/compute/CMakeLists.txt

example/lapack_to_chameleon/step6.h

include/chameleon.h

include/chameleon/runtime.h

include/chameleon/runtime_struct.h

include/chameleon/struct.h

runtime/openmp/control/runtime_descriptor.c

runtime/openmp/control/runtime_descriptor_ipiv.c

runtime/parsec/control/runtime_descriptor.c

runtime/parsec/control/runtime_descriptor_ipiv.c

runtime/quark/control/runtime_descriptor.c

runtime/quark/control/runtime_descriptor_ipiv.c

runtime/starpu/codelets/codelet_map.c

runtime/starpu/codelets/codelet_zgersum.c

runtime/starpu/codelets/codelet_zlacpy.c

runtime/starpu/control/runtime_async.c