Split Hgraph in smaller files and add mli
.gitignore: *.orig
Fixpoint rewriten to have a Stack parameter

Some tests are failing
returns bottom if no value is assigned to a vertex (rather than failing...)
Fix tests: recorver the real output vertices
Call abstract_init with the original vertex
Don't forget nodes from function graphs

Test_data is passing again
fix test_hgraph
Merge pull request #1 from chambart/master

Fixpoint with a stack
This allows widening, plus it has a flexible handling of the callstack.