partest: correct line numbers in run stack traces

partest adds a warning in a comment at the beginning of source files
that it copies, but this means that every line number displayed in a
stack trace is offset by 6. We can workaround this by making the warning
a single line with no newline at the end.

Author: smarter

test/test/CompilerTest.scala

@@ -438,12 +438,8 @@ abstract class CompilerTest {
     processFileDir(sourceFile, { sf =>
       if (extensionsToCopy.contains(sf.extension)) {
         dest.parent.jfile.mkdirs
-        dest.toFile.writeAll("/* ==========================================\n",
-                             " * ========= AUTOMATICALLY GENERATED ========\n",
-                             " * ========= DO NOT EDIT THIS FILE ==========\n",
-                             " * ==========================================\n",
-                             " * Original: " + sf.toString + " */\n\n",
-                             sf.slurp())
+        dest.toFile.writeAll("/* !!!!! WARNING: DO NOT MODIFY. Original is at: $sf !!!!! */",
+          sf.slurp())
       } else {
         log(s"WARNING: ignoring $sf")
       }

tests/run/origins.check

@@ -1,6 +1,6 @@
 
 >> Origins tag 'boop' logged 65 calls from 3 distinguished sources.
 
-     50   Test$.$anonfun$f3$1(origins.scala:22)
-     10   Test$.$anonfun$f2$1(origins.scala:21)
-      5   Test$.$anonfun$f1$1(origins.scala:20)
+     50   Test$.$anonfun$f3$1(origins.scala:16)
+     10   Test$.$anonfun$f2$1(origins.scala:15)
+      5   Test$.$anonfun$f1$1(origins.scala:14)