New parameters that exclude uncompatible numpy features

[bonelli]

While working on a SAV file I discovered that:

• columns with duplicated labels (titles) break the numpy implementation, but they are allowed in SAV files. Added an option that ignores labels (titles)
• certain date-time formats break reading uncompressed files directly with numpy. Added an option that forces using the usual iterator based reader, which works just fine.

Sadly I cannot post the test SAV file, it contains private data.

If you could release a new version with these new options, it'd be awesome, I could use them straight away.