Update eudat.re

Added functionality for checksum recomputation -setting the checksum date.
New function: EUDATiCHECKSUMdate, functions modified: EUDATiCHECKSUMretrieve, EUDATiCHECKSUMget
EUDATSetiCHECKSUMdate.r

The rule sets date of iCHECKSUM for all checksumed data objects, that doesn't have this set. It is intended to be run once on iRODS server that not supported iCHECKSUM periodic verification mechanism before.
Update EUDATSetiCHECKSUMdate.r
Merge pull request #13 from EUDAT-B2SAFE/checksum-verify

Checksum verify