Better dependency node printing.

Author: David Ungar

Tests/SwiftDriverTests/IncrementalCompilationTests.swift

@@ -496,7 +496,7 @@ final class IncrementalCompilationTests: XCTestCase {
         "Forming batch job from 1 constituents: main.swift",
         "Incremental compilation: Queuing Compiling main.swift",
         "Starting Compiling main.swift",
-        "Incremental compilation: Traced: interface of main.swiftdeps from: main.swift -> interface of top-level name foo from: main.swift -> implementation of other.swiftdeps from: other.swift",
+        "Incremental compilation: Traced: interface of source file 'main.swiftdeps' from: main.swift -> interface of top-level name 'foo' from: main.swift -> implementation of source file 'other.swiftdeps' from: other.swift",
         "Incremental compilation: Queuing because of dependencies discovered later: {compile: other.o <= other.swift}",
         "Incremental compilation: Scheduling discovered {compile: other.o <= other.swift}",
         "Finished Compiling main.swift",
@@ -520,7 +520,7 @@ final class IncrementalCompilationTests: XCTestCase {
         "Incremental compilation: May skip current input: {compile: other.o <= other.swift}",
         "Incremental compilation: Queuing (initial): {compile: main.o <= main.swift}",
         "Incremental compilation: scheduling dependents of main.swift; -driver-always-rebuild-dependents",
-        "Incremental compilation: Traced: interface of top-level name foo from: main.swift -> implementation of other.swiftdeps from: other.swift",
+        "Incremental compilation: Traced: interface of top-level name 'foo' from: main.swift -> implementation of source file 'other.swiftdeps' from: other.swift",
         "Incremental compilation: Found dependent of main.swift: {compile: other.o <= other.swift}",
         "Incremental compilation: Immediately scheduling dependent on main.swift {compile: other.o <= other.swift}",
         "Incremental compilation: Queuing (dependent): {compile: other.o <= other.swift}",