* Add latest version of libpng

* ncview depends on libpng

This closes #1308, where fetching a non-expanded resource from a mirror
will cause an error.

This also ensures that when a URL resource is fetched from a mirror,
that it will be named as though it were retrieved from the original
URL. This is particularly useful for non-expanded resources since it
ensures that the resource name is consistent for the installation
(this is less important for expanded resources because the build takes
place inside the expanded resource).

+ Starting with version 2.0, OpenMPI no longer provides C++ bindings by default
  (libmpi_cxx.so). Add a configure option to instruct the build to also build
  and install libmpi_cxx.so.
+ This MPI feature is needed by at least one spack package (moab).

plumed : avoid linking with libgslcblas

fix : ('build',) type dependencies are not accounted when autoloading

fixes #1681

fix a missing include in booststrap.
found on debian 8 with python 2.7

* pexsi : added package
* cp2k : added pexsi (works for gcc+openmpi with and without plumed)

Make libiconv work with C11

Globus Toolkit

- moved ensure_dicts() call from Package.__init__ to
  Package.__metaclass__.

Fix vim package.

Add sbt (scala build tool) package

* add pango dependency

* add new package ghostscript-fonts & add to ImageMagick as dependency

also tell ImageMagick's configure where the font dir is!

* refactor to fix flake8

* add homepage to ghostscript-fonts

* use install_tree

* remove unneeded import

Add two famous old versions of autoconf

These old versions are often used because their immediate successors are incompatible in some way.

C11 does not provide gets() any more, so we cannot reference it

Fix hash collisions, add stable hashing

- only output basic lists, dicts, etc.
- spec and database now parse and write specs as ordered data.

- Spec._dup() incorrectly copied cached hashes and normal/concrete values
  even when dependency structure was not preserved.

- Now these are only copied when *all* dependencies are copied.

- Currently, build dependencies are not currently hashed; we are waiting
  to hash these until we have smarter concretization that can reuse more
  installed specs.  The layout needs to account for this when checking
  whethert things are installed.

[WIP] Faster database loading, faster in-memory hashing

Add git-lfs package.

Fix dependency bug with `spack reindex`. 

- Transaction logic had gotten complicated -- DB would not reindex when
  corrupt, rather the error would be reported (ugh).

- DB will now print the error and force a rebuild when errors are
  detected reading the old databse.

- Spack currently not hashing build deps (to allow more reuse of packages
  and less frequent re-installing)

- Fast in-memory hash should still hash *all* deptypes, and installed
  specs will only reflect link and run deps.

- We'll revert this when we can concretize more liberally based on what
  is already installed.

- can now pass these to Spec.copy() and Spec._dup():
  - deps=True
  - deps=False
  - deps=(list of deptypes)

- Makes it easy to filter out only part of a spec.

- use a 3-pass algorithm to load the installed package DAG.

- avoid redundant hashing/comparing on load.