Ref. #241 - Fixes `sizes` demo markup.
Fixing `sizes` demo.
return a picturefill as a noop if <picture> is implemented
Merge pull request #269 from tylerball/feature/noop

return a picturefill as a noop if `picture` is implemented
Closes #264.
Restores support for `calc` in `sizes`.
Test to back up 6077274
source src attribute warning
adding a check for console undefined
Fix demo markup.
Closes #215 - Find all `img`, look for `picture` parent, and parse `source` elements *until* reaching the `img` that triggered everything. This matches the invalid case outlined in the note on http://picture.responsiveimages.org/#update-source-set .
Properly polyfills the extended `srcset`, assuming the default `sizes` value of `100vw`.
Merge branch 'sourcesrc-notification' of github.com:jcutrell/picturefill into jcutrell-sourcesrc-notification

Conflicts:
	tests/index.html
Editing warning message.
Merge branch 'jcutrell-sourcesrc-notification'
Merge.