add support for extracting .xz, .tar.xz and txz files
don't use 'x' arg when piping to tar
don't use 'x' arg when piping to tar
use --stdout with unxz to pass unzipped pkg to tar via pipe
Merge branch 'tar.xz' into develop

Conflicts:
	easybuild/tools/filetools.py
add support for mpi wrapper commands for QLogic MPI and MVAPICH2
Merge branch 'develop' into mpi_cmd_mvapich2

Conflicts:
	easybuild/tools/toolchain/mpi.py
Merge pull request #497 from boegel/mpi_cmd_mvapich2

add support for mpi wrapper commands for QLogic MPI and MVAPICH2