Refactored SQL in the Infinium database wrapper to handle rescans more
effectively. Also removes some SQL redundancy and reduces the number
of queries to the LIMS.

The LIMs wrapper now returns mapped NFS paths for files, so that the
path munging happens in one place only.

Fixed some documentation typos.
Merge pull request #278 from keithj/devel

Refactored SQL in the Infinium database wrapper to handle rescans