gitbase: remove git.Log from index commit iterator
gitbase: remove git.Log from index commit iterator

Fixes #769

git.Log was being passed as commit iter to the index iterator, but
the new commitIter should be passed instead. That generated a
discrepancy between the results of indexes and the sames queries
with no indexes.

Signed-off-by: Miguel Molina <75004f149038473757da0be07ef76dd4a9bdbc8d@erizocosmi.co>

gitql/gitql,gitql/gitql