Bugfix GetHashofDirs

GetHashofDirs would calculate an incorrect hash on directories with `.DR_Store` etc; now it only scans by default *xml files.
what_to_hash is the correct pattern to use

Signed-off-by: Fotis Georgatos <fotis.georgatos@uni.lu>
Merge pull request #969 from fgeorgatos/fix_GetHashofDirs

Bugfix GetHashofDirs