SI-6440 Address regressions around MissingRequirementError

 Go back to using globalError to report when a stub's info is referenced,
 and only throw the MissingRequirementError when compilation really
 must abort due to having a StubTermSymbol in a place where a
 StubClassSymbol would have been a better choice.

 This situation arises when an entire package is missing from the
 classpath, as was the case in the reported bug.

 Adds `StoreReporterDirectTest`, which buffers messages issued
 during compilation for more structured interrogation. Use this
 in two test for manifests -- these tests were using a crude means
 of grepping compiler console output to focus on the relevant output,
 but this approach was insufficient with the new multi-line error
 message emitted as part of this change.

 Also used that base test class to add two new tests: one for
 the reported error (package missing), and another for a simpler
 error (class missing). The latter test shows how stub symbols
 allow code to compile if it doesn't the subset of signatures
 in some type that refer to a missing class.

 Gave the INFO/WARNING/ERROR members of Reporter sensible
 toString implementations; they inherit from Enumeration#Value
 in an unusual manner (why?) that means the built in toString of
 Enumeration printed `Severity@0`.

1 files changed, 9 insertions, 3 deletions

diff --git a/src/compiler/scala/tools/nsc/reporters/Reporter.scala b/src/compiler/scala/tools/nsc/reporters/Reporter.scala
index c5321dd728..8871ae6555 100644
--- a/src/compiler/scala/tools/nsc/reporters/Reporter.scala
+++ b/src/compiler/scala/tools/nsc/reporters/Reporter.scala
@@ -20,9 +20,15 @@ abstract class Reporter {
   class Severity(val id: Int) extends severity.Value {
     var count: Int = 0
   }
-  val INFO    = new Severity(0)
-  val WARNING = new Severity(1)
-  val ERROR   = new Severity(2)
+  val INFO    = new Severity(0) {
+    override def toString: String = "INFO"
+  }
+  val WARNING = new Severity(1) {
+    override def toString: String = "WARNING"
+  }
+  val ERROR   = new Severity(2) {
+    override def toString: String = "ERROR"
+  }
 
   /** Whether very long lines can be truncated.  This exists so important
    *  debugging information (like printing the classpath) is not rendered