SI-7439 Avoid NPE in `isMonomorphicType` with stub symbols.

`originalInfo` can return null for stub symbols; deal with that
as we used to before a regression in 016bc3db.

After this change, we can once again delete A_1.class and still compile
code instantiating B_1. (A_1 is only referred to in a method signature
of B_1 which is not called from our code.)

	scala> new B_1
	warning: Class A_1 not found - continuing with a stub.
	res0: B_1 = B_1@5284b8f9

In practice, this situation arises when someone uses a third
party class that was compiled against other libraries not avaialable
on the current compilation classpath.
SI-7292 Fixes test failures by updating *.check files

Looks like partest's confusion about / vs. \ was fixed between
the original Jenkins run of the fix for SI-7292 and its merge.
Merge pull request #2668 from soc/SI-7292-fix

SI-7292 Fixes test failures by updating *.check files
SI-7433 Fix spurious warning about catching control throwable

In the same vein as SI-6994, we have to be careful not to warn
about synthetic code. In that case, the spurious warnings came
because we warned in the typechecker, which was also called in
erasure. In this case, we are issuing the warning in Uncurry,
so we must be mindful of the pattern matchers translations of
non-trivial catch patterns, which look like:

    case (ex8 @ _) => {
    <synthetic> val x5: Throwable = ex8;
    case11(){
      if ({
        case14(){
          if (x5.$isInstanceOf[NullPointerException]())
            matchEnd13(true)
          else
            case15()
        };
        case15(){
          if (x5.$isInstanceOf[RuntimeException]())
            matchEnd13(true)
          else
            case16()
        };
        case16(){
          matchEnd13(false)
        };
        matchEnd13(x: Boolean){
          x
        }
      })

This commit detects that `ex8` is synthetic and disables the warning.
Merge pull request #2637 from retronym/ticket/7439

SI-7439 Avoid NPE in `isMonomorphicType` with stub symbols. …
Merge pull request #2653 from retronym/ticket/7433

SI-7433 Fix spurious warning about catching control throwable