Add a patch to silence some Boost compiler warnings

Add a patch to silence some Boost compiler warnings that clog up the build output of some packages (such as piranha).

The first chunk of the patch has already been merged for boost > 1.55, and will need to be removed for future Boost versions.

The second and fourth chunks are simply additions of ``static_cast`` to an implicit conversion, and as such should not change anything functionally.

The third patch uses the GCC pragma support to silence a warning only for two specific lines of source code. It is supposed to work with GCC >= 4.6 (hence the ``#ifdef`` guards). Testing with GCC 4.6 and older would be much appreciated.

This patch silences all warnings in piranha, but some warnings still exist while compiling boost.