remove most traces of boost::regex

remove most traces of boost::regex

1/ remove boost regex code from 3rdparty/boost. Only the cmake stuff remains.

2/ remove traces of BOOST_LIB since there is no need anymore to
   compile boost stuff.

3/ remove traces of boost regexp in config/lyxinclude.m4 and INSTALL

4/ require gcc 4.9 as minimal version in autoconf.

Unfortunately, the net gain is only 10% of included boost size (now 21M).