Experimental modification of forward analysis and rewrite

This implementation discards graph entries passed in by the user
and uses factbase passed in to analysis to get the list of known
entry nodes. Note: this forces user to actually pass in facts
about all entry points he wants analysed or else they will be
discarded in the rewritten graph. Previously bottom was assumed
implicitly.
Remove entries for arbGraph
Clean up forward analysis
AnalyzeForwardBlocks modified
Rewrite last of the hoopl functions using Entries
Pass initial facts in liveness and info tables
Expect that entry fact always exists
Remove joinInFacts, change getFact

joinInFacts was used only for debugging, getFact now assumes that
fact must be present in the factbase - otherwise it panics