add mvapich2 package to handle different compilers and variants
add lwgrp package
adding dtcmp package
cannot uninstall dtcmp because depends on dtcmp
fileutils package
add libcircle package
adding libarchive
More descriptive error when package constructor fails.

- helps package_sanity test identify which package failed.
- encountered while upgrading versions in Adam's packages to the new format.
Fix up versions to match new version format, minor formatting.
Merge branch 'develop' into features/fileutils

Conflicts:
	lib/spack/spack/packages.py
Add command to show packages added in particular git revisions.

spack pkg list    [rev]           list packages for revision.
spack pkg diff    [rev1] [rev2]   diff bt/w packages in rev1 and rev2
spack pkg added   [rev1] [rev2]   pkgs added since rev1
spack pkg removed [rev1] [rev2]   pkgs removed since rev2
update libcircle to download tarball from github/hpc
Support for pkg-config.
Fileutils successfully finds libarchive; can't find dtcmp despite config arg.
Take fileutils out and just merge the deps into develop.
Merge branch 'features/fileutils-deps' into develop