[oe] linux-omap3_git.bb doesn't work when copied to user.collection

[Elvis Dowson]

Hi Phil,
		I think I know how this might have happened. While developing a new  
recipe based on linux-omap3_bit.bb, I aborted a download, once I saw  
that it was working.

After that, all subsequent attempts were trying to probably use that  
aborted tar ball and extracting the git repository and that repository  
probably was corrupted or something.

Can OE be enhanced to avoid this situation, by comparing the checksum  
of the tar ball, before attempting to extract and use it?

Best regards,

Elvis