Add poster frame attribute to video() helper
Bug 905347
Use video() helper for videos across bedrock
Bug 905348
Bug 832348: Redirect all default documents (index.html) to the folder.
Remove mutable default argument from platform_img

See http://effbot.org/zone/default-values.htm for decent explanation of
why this is bad.

Also added tests.
Merge pull request #1173 from jgmize/remove-mutable-default-arg-platform_img

Remove mutable default argument from platform_img
Merge pull request #1166 from sgarrity/bug-905348-video

Add poster frame attribute to video() helper and use the video() helper across bedrock
Fix typo in fx/performance screencast ogv video URL.
Merge pull request #1172 from pmclanahan/redirect-index-html-bug-832348

Bug 832348: Redirect all default documents (index.html) to the folder.