* error.c, internal.h (rb_bug_reporter_add): add a new C-API.
  rb_bug_reporter_add() allows to register a function which
  is called at rb_bug() called.
* ext/-test-/bug_reporter/bug_reporter.c: add a test for this C-API.
* ext/-test-/bug_reporter/extconf.rb: ditto.
* test/-ext-/bug_reporter/test_bug_reporter.rb: ditto.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43303 b2dd03c8-39d4-4d8f-98ff-823fe69b080e