buffer instead of an std::ostringstream.  This way logging doesn't cause
memory allocations.  This breaks backwards compatibility with the previous
hook function API but only slightly.  The new hook functions must take a
const char* instead of std::string.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403395