Fix exception-handling feature with gcc.jam

  see: https://svn.boost.org/trac/boost/ticket/5293
Fix linker flags with clang

  see: https://svn.boost.org/trac/boost/ticket/5820
Fix infinite loops in regex.replace

  see: https://svn.boost.org/trac/boost/ticket/7176
Check BJAM_NO_MEM_CACHE switch
Make clang-linux actions better
Fix incorrect type