spack graph improvements

- fix deptype support
- by default, graph command omits build depedencies
- update docs to use deptype args

- Fixed logic for collapsing backward edges

- Last collapse now depends on whether prior step in left collapse
  sequence alrady did the collapse.

- Distinguish between static (package) and dynamic (spec) graphs.

  - static graphs ignore conditions and multiple instances (hashes) and
    plot raw dependencies among packages.

  - dynamic graphs include information from particular specs (instances of
    packages) and can have multiple instances with hashes.

- Allow graphing all packages in the install DB.

  - useful for debugging.

Don't set cpp when building on Darwin.

* atlas: fix unit test

* openblas: remove symlinks; use lapack_libs.ld_flags in the test

* mkl: fix openmp variant of blas/lapack libs

* intel-parallel-studio: fix openmp variant of blas/lapack libs

* netlib-scalapack: fix blas/lapack for multilib case (e.g. mkl)

* arpack-ng: fix blas/lapack for multilib case (e.g. mkl)

* petsc: explicitly specify blas/lapack

* minor

* cantera: fix blas/lapack usage

* ipopt: fix blas/lapack usage

* netlib-lapack: fix external blas usage

* mfem: fix lapack/blas usage

* superlu-mt: fix blas usage

* flake8 fixes

* Remove duplicate ICU package

* Ignore deleted files during flake8 tests

* Rename Boost ICU variant

* m4: fix compilation on Sierra with GCC

* m4: check macOS version

This is a security update with priority "HIGH".

* dealii: add missing python dependency

* boost: fix a bug which  broke it on macOS with clang+gfortran

Boost was using gcc compiler instead of clang++, which lead to
cryptic Undefined symbols linking errors for boost::python::objects::function_object()
when building other packages against boost+python.

* boost: add exceptions for intel

* boost: use spack_cxx

* Perform shebang fix for all files

* Fix sbang for perl scripts

Otherwise perl would look at the #! line and call sbang again, resulting
in an infinite loop.

* Removed SPACK_DIRTY env var support.

* Finished removing SPACK_DIRTY support.

* Minor changes.

* Turned <provider>_libs into an iterable

Modifications :
- added class LibraryList + unit tests
- added convenience functions `find_libraries` and `dedupe`
- modifed non Intel blas/lapack providers
- modified packages using blas_shared_libs and similar functions

* atlas : added pthread variant

* intel packages : added lapack_libs and blas_libs

* find_library_path : removed unused function

* PR review : fixed last issues

* LibraryList : added test on __add__ return type

* LibraryList : added __radd__ fixed unit tests

fix : failing unit tests due to missing `self`

* cp2k and dependecies : fixed blas-lapack related statements in package.py

Add package for bedtools2, with support for v2.25.0 and v2.26.0.

bamtools provides a C++ API & command-line toolkit for working with BAM
data.

Python will look to link with libncursesw in preference to libncurses. Since
ncurses in spack is built without suffixes there is no libncursesw and
python will link to the system libncursesw for _curses.so and
_curses_panel.so, as well as libpanelw for _curses_panel.so.

This PR introduces a patch that simple removes the check for ncursesw in
setup.py and therefore sets `curses_library` to `ncurses`.