* thread.c (update_coverage): skip coverage count up if the current
	  line is out of the way.  rb_sourceline() is unreliable when source
	  code is big.  [ruby-dev:44413]

	* test/coverage/test_coverage.rb: add a test for above.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@34181 b2dd03c8-39d4-4d8f-98ff-823fe69b080e