swift234

- Diagnose conditional PBD's without an else, conditional ones that do have an else,
  and refutable pattern bindings without an initializer.
- Enhance ASTDumper to dump where/else clauses on PBDs.
- Merge if/let conditional PBD logic into the mainline logic now that they are all
  potentially conditional (more simplifications coming for this)

add tests for the fixits, which exercise the earlier SourceRange enhancments, e.g.:

x.swift:3:5: error: refutable pattern match can fail; add an else {} to handle this condition
let o? = a
    ^~
           else {}




Swift SVN r26751