progress towards removing ProjectionSpec
add Sybase support (using existing SQL Server support, which should work for Sybase)
fix check for modified mapping file in D2R Server
improve behaviour of fixed-length string columns for trailing spaces
improve docs regarding d2rq:alias
fix small bug in new CHAR handling, and update tests accordingly
improve error reporting for startupSQLScript errors
fix some logic around AliasOp and projections
many optimizations and fixes for optree building, duplicate/unique key handling, etc
More refactoring:

- get rid of ProjectionSpec
- split ExtendOp off ProjectOp
- extract some superclasses in db.expr package
Merge branch 'refactor-projectionspec' into develop