Uploading a txt file with XML contents makes GDrive return the XML mime
type.
This fix makes sure the logic that returns "SPACE_UNKNOWN" for the size
properly rely on the Google Docs mime types.
Whenever a file is uploaded to GDrive, there is a check for that file
with and without extension, due to Google Docs files having no
extension. This logic now only kicks in whenever the detected
extensionless file is really a Google Doc file, not a folder.
This makes it possible again to upload a file "test.txt" in a folder
that also has a folder called "test"
