FIX: cleanMetadataCatalog signature

The signature was not right
lower()
in getStorageElementSiteMapping() return only sites with non-empty list
of SEs
Restored the dropped logic of using proxy SEs
Fix the UseProxy LocalSite option
Merge pull request #1313 from sposs/patch-44

FIX: cleanMetadataCatalog signature
v6r6p21
Conflicts resolved after merging with rel-v6r6
Merge pull request #1315 from fstagni/fixExtendTransf

FIX: lower() when comparing
Merge pull request #1316 from atsareg/fix-v6r7

[v6r7] Several fixes
v6r7p13
Merge remote-tracking branch 'upstream/rel-v6r7' into rel-v6r7