midification on BasicBlock and BlockEdge related structures for reverse
dominance frontier computation.
and implement function to add augmented block for all functions and main
routine

next steps:
1. implement remove augmented block function
2. reverse domination analysis
3. dominance frontier computation
implemeted remove augmented blocks function
(without reverse-dom related fields)
implemented reverse dominance computation related functions in df.c
start implemeting dominance frontier computation
finished reversed dominance frontier computation, not fully tested yet.
simple testcases are correct.

next step:
generalize forwad and backward slicing funtions
fixed some bugs in syntax.c
1. add throw and try-catch related structures into syntax tree.
2. add funtions generating decision vector and signature functions. (not
done)
3. none of above is tested.
fixed bugs in reversed dominance frontier computation.

finished signature function generation functions except insert
checkPoints
nothing, really
fixed bug in dominance frontier computation. add comments for modified
forward slicing algorithm.
backward slicing
implemented slicing functions.
add flags in arrayList
not fully tested
implemented insertCheckPoint function. we adopted a lazy approach, such
that no AST node is inserted for check point, instead, all relies on the
printSyntaxTreeNode() function to handle information stored in nodes
correctly. therfore, changed all data structure and functions
accordingly.

NOTE: problem introduced by missing branch code in trace...
fixed a bug in printSyntaxTreeNode() for the output of checkpoints.
add copyright header