QR method: Fixed implementation and tests for non-symmetric matrices.
SVD: Fixed flaw in test.

Since ViennaCL-matrices are now padded by default, one use of fast_copy() was malformed.
OpenMP: Fixed use of unsigned integer type for outer loop in matrix-matrix products.
libviennacl: Added GEMM for host, CUDA, and OpenCL (no tests yet).

This completes the features for the 1.5.0 release.
Additional BLAS level 3 functionality as well as access to algorithms will be added later.
libviennacl: Added extensive tests for GEMM and fixed a couple of interfacing bugs.
libviennacl: Cleanup: Applied pimpl-idiom to separate implementation from viennacl.hpp

This way one can keep viennacl.hpp unchanged and deal with all the details internally.
Host/CUDA/OpenCL backends are no longer globally visible, but instead hidden in a common backend.
Backend objects are now explicitly created and destroyed, added minimal API for this.
Fixed unused variable warning.
Fixed a bunch of (mostly conversion) warnings on VS Studio 2013.
AMG: Fixed OpenMP warnings obtained on GCC 4.1.2
AMG: Fixed second round of OpenMP warnings obtained on GCC 4.1.2
Generator: Removed unused generator_segmentation as well as boost/foreach.hpp includes in tests.
QR-method, SVD: Initialization of ublas-vectors through scalar_vector rather than directly in CTOR.

The CTOR-initialization is not supported with older uBLAS versions (e.g. 1.33),
hence using this more robust implementation.
Various minor fixes for GCC 4.2.1 and Boost 1.33 when using -Wextra
Generator: Removed uses of .at() member on a std::map<>, since this is only available in C++11.
Autotuner: Replaced uses of .at() for std::map<> (C++11) with a C++03-compatible implementation.
Generator: Fixed warnings obtained with Clang 3.3.

Two unused member variables and one potential use of an uninitialized variable.
AMG: Fixed warnings obtained on Visual Studio 2013 (all integer conversion warnings).
AMG: Fixed more VS 2013 conversion warnings including a bug introduced by previous commit.
Visual Studio 2013: Fixed various minor conversion warnings.
Doxygen: Fixed all warnings (required some refactoring in generator)

It seemed like Doxygen had some troubles with some symbol shortcuts
obtained from 'using namespace ...' in the generator implementation.
Hence, I removed these using-declarations and added full namespaces to the respective type names.