Work around bug 1098470 by detecting manifest.* with getFeature (bug 1097424)

In Firefox OS 2.0 and 2.1 (possibly 2.2 if the bug isn't fixed soon),
hasFeature(manifest.*) will fail, but getFeature(manifest.*) will work.
Merge pull request #824 from diox/workaround-has-feature-manifest-yulelog

Work around bug 1098470 by detecting manifest.* with getFeature (bug 1097424)