Copyright (c) 2012 Kevin Wellwood
All rights reserved.
This source code is distributed under the Modified BSD License. For terms and
conditions, see license.txt.
Extracts a readable Ada unit name from a source reference line. If the
source reference doesn't contain symbols then an empty string will be
returned because the unit name can't be determined.
Returns the value of 'point' as it would be snapped to a grid of size
'gridSize'. If 'centered' is True, the snap will occur in the middle of
the grid lines instead of on them.