Convert Redundant to multi-entry.

No significant difficulties with the conversion.
Convert Useless to multi-entry.

No significant difficulties with the conversion.
Cosmetic improvments to Analyze and Analyze2.
Cosmetic improvements to SSA and SSA2 IL.

Take advantage of the revision of the type of the 'main' field in
{SsaTree,SsaTree2}.Program.T from "FuncEntry.t" to
"{entry: FuncEntry.t, func: Func.t}" made by commit 1f6e6a.
Convert Flatten to multi-entry.

No significant difficulties with the conversion.