warn about if and iterate on the element's template

Review URL: https://chromiumcodereview.appspot.com//12541013
bump pubspec
Re-enable analyzer in output generated by dwc. Also fix a couple warnings, and
print a better error message when DRT fails.

Review URL: https://chromiumcodereview.appspot.com//12607004
Attempting to optimize a couple of web_ui list operations.

The tree traversals happen fairly often and during profiling I was seeing a decent amount of garbage being generated. Attempting to minimize garbage.

BUG=

Review URL: https://chromiumcodereview.appspot.com//12388049
allow custom-tags-with-dashes

BUG=

Review URL: https://chromiumcodereview.appspot.com//12482003
fixes #236, import of component dart files.
we just need to track things that are referenced from html files as modified.

Review URL: https://chromiumcodereview.appspot.com//12645003
bump version
bump versions
update changelog for 0.4.1+x stuff
add hashCode to Change* types, fixes #372

Review URL: https://chromiumcodereview.appspot.com//12606003
merged