[boost] Misbehaviour of boost.regex

Hi *, I think I stumbled across a bug in boost.regex, but perhaps it is just me misunderstanding the docs. Basically it seems like regex_match breaks its postcondition when working with std::string input and smatch result. Attached is a new test case for the test suite (my first trial, I bet it does not fit into boost unchanged) which shows the bug (if it is one). Interestingly, using regex_match together with a const char pointer and cmatch results works like expected. I attached the new source file, which belongs into boost/libs/regex/test/regress together with changes to the Jamfiles as a diff. Any comments welcome. Greetings Torsten