* error.c (name_err_mesg_to_str): clear rb_thread_t::errinfo when
	  ignore exception under rb_protect().

	* test/ruby/test_exception.rb (test_exception_in_name_error_to_str):
	  add a corresponding test.
	  ignore exception under rb_protect(). [ruby-core:41612] [Bug #5755]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@34466 b2dd03c8-39d4-4d8f-98ff-823fe69b080e