optimizations in deduction phase

[rajdeep87]

This commit contains the following optimizations:

1. A new implementation for storing the lower and upper bounds for Intervals corresponding to numerical variables. Use BOX macro for using this optimization. This is implemented in method update_var_bound() in acdl_domaint. The benefit is that it replace the method is_subsumed_syntactic(). The implication graph stores a new deduction only if it updates the corresponding bounds (upper or lower).
2. Generate templates for numerical variables and boolean variables only when the corresponding num_vars and bool_vars respectively is non-empty.
3. Use NO_PROJECTION for boolean and numerical inferences.
4. For arithmetic statements such as z=x*y, process the statement only when both the operands are available.
5. For numerical inference, do not generate templates on variables that appears in the old_value. This optimization is only needed for INTERVALS. For Octagons, turn OFF this optimization by using the OCTAGONS macro in acdl_domaint.
6. For equality statements such as x==y, process the statement only when the value of either operand is known. Use the INTERVAL macro do turn on this optimization in acdl_solver.cpp
7. Turn off the calls to preprocess_val() since an equality statement such as (x==N) which can only come from assumption statements is never inserted directly into the trail.