Do not attempt to validate index_page

index_page is stored as-is in the dashIndexFilePath plist key,
and it is therefore a relative value, so there is no point in
validating it against the cwd and the filesystem, at least not
at this level.
Remove the not existing index page test (see #22)
Merge pull request #22 from FiloSottile/patch-1

Do not attempt to validate index_page