Update the bundled boost copy from 1.56 to 1.62.

Update the bundled boost copy from 1.56 to 1.62.

This commit updates our bundled copy of boost from 1.56 to 1.62. While
doing this I removed several boost libraries that are not used anywhere
in deal.II nor in the rest of the part of boost that we bundle:

boost/compatibility: This little library wraps the standard C headers
and we don't need it.

boost/signals: This has long since been deprecated in favor of
signals2.

boost/tr1: The boost TR1 library contains reimplementations of features
that ultimately appeared in C++11. We implement this ourselves with the
std_cxx11 namespace so we skip this folder.

boost/thread/experimental: This library is new and we don't currently
have any use for it.