An ebuild for deal.II [1]

This commit introduces an ebuild for the deal.II library.

[1] http://www.dealii.org/

 "deal.II is a C++ program library targeted at the computational solution of
  partial differential equations using adaptive finite elements. It uses
  state-of-the-art programming techniques to offer you a modern interface to the
  complex data structures and algorithms required."
Improve dealii-9999.ebuild to be more consistent with Gentoo's best practices

Specifically:

  - Rename use flags thread -> tbb, umfpack -> sparse as match common practice
  - Add virtual/pkgconfig to DEPEND
  - Remove double occurence of sys-libs/zlib
  - Provide a static-libs use flag
Clean up the documentation installation: Only install html files if +doc is set
use "${BUILD_DIR}" instead of "${WORKDIR}"/${P}_build
Simplify
Bugfix: Get the dependencies with mpi right. Add REQUIRED_USE constraints
Install the examples properly to usr/share/doc/${PF}/examples
Bugfix: trilinos unconditionally installs with mpi support enabled.
Fix typo
Merge pull request #96 from tamiko/package-dealii

An ebuild for deal.II [1]