Boost is updated to a more recent version to avoid many compilation
warnings. However, boost 1.76 introduces a brand new regex library.
Therefore, it was chosen to use the last version before that to
minimize changes.
The part that adapts our source to the new boost requirements is
backported from 09130d7a62.
icu.{hpp,cpp} is not needed and cannot be compiled since it depends on libicu.
The other two files are currently not used, but could be in principle, so I
added them to the build.
Boost.Signals is deprecated. This fixes bug #9943.
The only thing left to do is to rewrite (or get rid of) the boost -mt test
in config/lyxinclude.m4 not to use signals anymore.
It turns out that it did not take off since introduced in 2011. It is better to remove it and the associated boost headers (extract.sh was run against boost 1.60 to do the update).
Since we will move away from several boost classes when transitioning to C++11, it is good to start by removing lesser used ones.
It is easier to use instead getVectorFromString for the use we have of this tokenizer. The two places are environment.cpp (path stuff) and qt_helpers (file fileters). The new code is much shorter.
This allow to remove boost/tokenizer.hpp and friends from our boost tree.
