Added regression test for InstanceTag#content_tag so that it can take a block
Added regression test for InstanceTag#content_tag so that it can take a block

dg1dd1ngs/haml,stanhu/haml,haml/haml,stanhu/haml,amatsuda/haml,sideci-sample/sideci-sample-haml,concord-consortium/haml,haml/haml,uniba/hamldoc_ja,tangposmarvin/haml,haml/haml,haml/haml,tangposmarvin/haml,nazar-pc/haml,macressler/haml,macressler/haml,keithpitty/haml,keithpitty/haml,dg1dd1ngs/haml,nazar-pc/haml