Regex: Set a limit on how many recursions we allow.

include/boost/regex/v4/perl_matcher.hpp

@@ -378,7 +378,7 @@ public:
       BidiIterator l_base)
       :  m_result(what), base(first), last(end), 
          position(first), backstop(l_base), re(e), traits_inst(e.get_traits()), 
-         m_independent(false), next_count(&rep_obj), rep_obj(&next_count)
+         m_independent(false), next_count(&rep_obj), rep_obj(&next_count), m_recursions(0)
    {
       construct_init(e, f);
    }
@@ -566,6 +566,8 @@ private:
    bool m_unwound_alt;
    // We are unwinding a commit - used by independent subs to determine whether to stop there or carry on unwinding:
    //bool m_unwind_commit;
+   // Recursion limit:
+   unsigned m_recursions;
 #endif
 
    // these operations aren't allowed, so are declared private,