remove very ugly lexical_cast hack with a slightly less ugly one

svn path=/trunk/boost/xpressive/; revision=77913
replace MPL assert with static assert since it's problematic in C++11, refs #6846

svn path=/trunk/boost/xpressive/; revision=78286
simpler, more std-compliant implementation of cpp_regex_traits, refers #7143

svn path=/trunk/boost/xpressive/; revision=79589
undo problematic [79589]

svn path=/trunk/boost/xpressive/; revision=79613
fix compile error on some msvc test runners

svn path=/trunk/libs/xpressive/; revision=79726
fix assertion in cpp_regex_traits on libc++, thanks to John Fletcher

svn path=/trunk/boost/xpressive/; revision=79732
op::as shouldn't assume string::iterator != char*

svn path=/trunk/boost/xpressive/; revision=79761
only string iterators point to contiguous data

svn path=/trunk/boost/xpressive/; revision=79763
work around buggy wide ctype facet on cygwin and mingw

svn path=/trunk/boost/xpressive/; revision=79765
make regress and c_traits tests smaller by factoring out wide-char tests

svn path=/trunk/libs/xpressive/; revision=79766
work around missing __isctype on some glibc implementations

svn path=/trunk/boost/xpressive/; revision=79789
turn off debug symbols on msvc

svn path=/trunk/libs/xpressive/; revision=80211
make sub_match work with boost.range, doc tweaks

svn path=/trunk/boost/xpressive/; revision=80300
fix erroneous use of BOOST_CONSTEXPR config macro

svn path=/trunk/boost/xpressive/; revision=80312
work around strange msvc bug

svn path=/trunk/boost/xpressive/; revision=80357
comment typo, refs #7554

svn path=/trunk/libs/xpressive/; revision=81153
disable anoying msvc-11 warnings during tests

svn path=/trunk/libs/xpressive/; revision=81154
accomodate recent changes to boost's smart pointers, refs #7809

svn path=/trunk/boost/xpressive/; revision=82103
make symbols test pass on gcc with -Wall

svn path=/trunk/boost/xpressive/; revision=82336
remove unused variables, refs #8039

svn path=/trunk/boost/xpressive/; revision=82832