Fixed cyanogenmod issue 2861: asset redirection breaks access to AndroidManifest.xml.

Themed asset managers lose the ability to access application assets
without a cookie because the search order favors most recently added
asset paths (theme apks are added last).  So, searching for
AndroidManifest.xml would always return the themes manifest, not the
application manifest.

The solution is to mark the themed asset path and ignore it when
searching for cookie-less assets.  This should not cause problems with
theme application because the theme uses resource identifier based
redirections which always retain the asset path cookie that is to be
used to load the final resource.