gitignore dirs like build.foo
harness: Truncate messages to one line
harness: Support more assertion types
Replace test_bindings.html with various content tests

Fixes #631.
Revise DOMParser test

This is commented out for now (as it was in test_bindings.html) because it
causes a task failure.  I'll open a ticket about that.
auto merge of #1070 : kmcallister/servo/test-bindings, r=jdm