EG/TS: started refactoring iter(Data) into a data-range and a sorted-list-of-keys methods.
EG/TS: left some ideas.
EG/TS: Sequential(Multi)Storage methods renamed

SequentialMultiStorage:
 - getMultiple -> getMultipleData

SequentialStorage:
 - iter -> range
EG/TS: using getMultipleData with ignoreMissing flag in OaiList.

Added ignoreMissing.
EG/TS: only retrieve non-deleted records from storage.
TS: removed no longer needed 'key == stop' check.
EG: fix for intercepting file I/O + fix for monotonic seeks