Bugfix: isomorphism check was not strict enough

Some non-isomorphic graphs were erroneously considered to be isomorphic. It could
happen that two different nodes were not compared as they've already been marked as
visited by some other comparisons. With this commit, a node comparison will be
skipped only if exactly the same nodes were already compared before.
Begin code generation implementation

Supports Add, Mul, Call, Return instructions
Make integration tests use the FIRM backend for now
Merge pull request #226 from jspam/074-codegen

Begin code generation implementation
Pass parameters in registers; make System.out.println and calloc work
Merge pull request #227 from jspam/075-codegen-println

Generate code for System.out.println and calloc
Merge pull request #212 from Stoeoef/bugfix-check-nodes-twice

Bugfix: isomorphism check was not strict enough
Add isomorphism matcher for assembler code
Code generation for control flow and Phis
Merge pull request #228 from jspam/076-codegen-phi

Begin code generation for control flow and Phis
Eliminate ExtendedInt
Merge pull request #229 from Kha/conv

Eliminate ExtendedInt and Iu
Move deleteDivOrMod from Optimization companion object to new GraphExtensions

It doesn't really have anything to do with Optimization
Loop strength reduction