A few tweaks to streamline command-line compilation.
Fixed a NPE bug in BasicSolver when WorldTreeFactory was initialized
with no definitions file
Merge branch 'working' into gurupras@buffalo.edu
Added comments to range package
Added validateDefinitions method to ConstraintSolver

This method is to be used before pushing down constraints
It ensures that all the constraints that have been defined, have
definitions at every lower level
Merge branch 'gurupras@buffalo.edu' of github.com:gurupras/worldtree into gurupras@buffalo.edu
Merge branch 'gurupras@buffalo.edu' into working
Fixed bugs in Expr class
    - Removed baseExpr field
    - Created Expr object expected to be baseExpr
Updated circular dependency exception message in BasicSolver
Fixed issue with BasicSolver implicitly choosing the underlying
property while aggregating

Example:
    DEFINE ROOM R.treasure as AGGREGATE SUM(REG.monster) in REGION REG;
While computing the value of R.treasure, the solver was implicitly
selecting REG.treasure instead of using the property provided