opt-in of full data integrity check in cvmfs_server check
run data integrity check in test cases
FIX: misleading variable name in swissknife scrub
do storage integrity check first
Merge pull request #351 from reneme/check_extended

Full Data Integrity Check as Opt-In in `cvmfs_server check`

This adds a -i option to cvmfs_server check to enable the full data integrity check provided by cvmfs_swissknife scrub. By default this is disabled.

Additionally the integration test cases run this check now be default.