CFGFast: do not traverse graph recursively in post-processing.
CFGFast: do not traverse graph recursively in post-processing.

We were traversing CFG recursively before due to this bug. This commit
makes CFG generation on complex binaries way faster than before.

f-prettyland/angr,tyb0807/angr,angr/angr,tyb0807/angr,angr/angr,axt/angr,chubbymaggie/angr,f-prettyland/angr,iamahuman/angr,schieb/angr,angr/angr,f-prettyland/angr,axt/angr,chubbymaggie/angr,tyb0807/angr,iamahuman/angr,iamahuman/angr,chubbymaggie/angr,schieb/angr,schieb/angr,axt/angr