The preprocessor now creates a tables.CArray for each column of a table (the table is kept intact and is used for the iterator). It is done by copying all the elements from each tables.Column. VirtualTrackColumn.as_numpy_array() now slices the CArrays instead of the table Columns.
Merge branch 'pytables' of github.com:brynjagr/gtrackcore into pytables

Conflicts:
	gtrackcore/preprocess/PreProcessTracksJob.py
	gtrackcore/preprocess/pytables/CommonTableFunctions.py