* lib/irb.rb: Prevent irb from crashing when exception with
  nil backtrace is raised.
  [fix GH-434][ruby-core:58078][Bug #9063]
* test/irb/test_raise_no_backtrace_exception.rb: ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47164 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* properties.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47165 b2dd03c8-39d4-4d8f-98ff-823fe69b080e