pts-to: make applyRule functions part of PointsToGraph

1) access to the private elements
2) testability
3) nothing, just don't see anything that should keep me from this
pts-to: make all insert* functions private

Only tests need them public, but test will use friend class that
will be introduced in following commits.
pts-to: add PTGTester class

this class has access to PointsToGraph private members and will serve
for testing
pts-to tests: move helper functions to PTGTester

keep tests in one file and generic functions in another
pts-to: move FixedCategories to tests

This class is used only in tests anyway
pts-to tests: add applyRule(s) to PTGTester

Allow PTGTester use apply rules
ptg tests: add offset to testing pointers

don't use offset -1 everywhere
ptg tests: add notTested helper function

Write message that something has not been tested and add
it to failed tests
ptg tests: add tests for applyRule's methods.
ptg tests: add null pointer

allow get null pointer via getPointer helper function
ptg tests: add PTG.insertDerefBoth
ptg tests: add more tests
ptg: fix applyRule(deref var asgn deref var)

I need to fix the graph from which I add the points-to pairs. (In the
case the topology of the graph is changed by the addition, I can not
use the new topology but I need to use the old one)