Add OpenMP for GCC on Unix
Start adding generic viennacl context wrapper
Add mem handle access to dense matrix and vector
Clean-up
Merge branch 'master' into platform-support

Conflicts:
	src/_viennacl/dense_matrix.h
Missed bits from merge
Stray deprecated param
Merge branch 'master' into platform-support

Conflicts:
	src/_viennacl/pyviennacl.hpp
	src/_viennacl/structured_matrix.hpp
	src/_viennacl/vector.hpp
More clean-up
Construct vcl vector with context
Wrap mem_handle
Fix pointer handling; add raw memory constructors for vector
Fixes for building without OpenCL; some clean-up
Reorganise iterative solvers so as to build elegantly both with and without OpenCL
Add handle and context to Vector, Node and Statement; enable constructing Vector with various contexts
Add memory handling to _viennacl sparse matrices and scalars; add compressed_compressed_matrix to _viennacl
Split compressed_matrix into cpu_compressed_matrix, compressed_matrix, and compressed_compressed_matrix
Add context and handles to PyViennaCL sparse matrices
Add context and handle to PyViennaCL scalars
Add context and handle to PyViennaCL dense matrix