SI-3368 CDATA gets a Node

XML Parser uses `scala.xml.PCData`.

A compiler flag `-Yxml:coalescing`, analogous to
`DocumentBuilderFactory.setCoalescing`, turns `PCData`
nodes into `Text` nodes and coalesces sibling text nodes.

This change also fixes parse errors such as rejecting a
sequence of CDATA sections.

A sequence of "top level" nodes are not coalesced.

```
scala> <a><b/>start<![CDATA[hi & bye]]><c/>world<d/>stuff<![CDATA[red & black]]></a>
res0: scala.xml.Elem = <a><b/>start<![CDATA[hi & bye]]><c/>world<d/>stuff<![CDATA[red & black]]></a>

scala> :replay -Yxml:coalescing
Replaying: <a><b/>start<![CDATA[hi & bye]]><c/>world<d/>stuff<![CDATA[red & black]]></a>
res0: scala.xml.Elem = <a><b/>starthi &amp; bye<c/>world<d/>stuffred &amp; black</a>
```

4 files changed, 70 insertions, 0 deletions

diff --git a/test/files/pos/t3368.flags b/test/files/pos/t3368.flags
new file mode 100644
index 0000000000..cb20509902
--- /dev/null
+++ b/test/files/pos/t3368.flags
@@ -0,0 +1 @@
+-Ystop-after:parser
diff --git a/test/files/pos/t3368.scala b/test/files/pos/t3368.scala
new file mode 100644
index 0000000000..c8e861a899
--- /dev/null
+++ b/test/files/pos/t3368.scala
@@ -0,0 +1,5 @@
+
+trait X {
+  // error: in XML literal: name expected, but char '!' cannot start a name
+  def x = <![CDATA[hi & bye]]> <![CDATA[red & black]]>
+}
diff --git a/test/files/run/t3368.check b/test/files/run/t3368.check
new file mode 100644
index 0000000000..1d9dd677f6
--- /dev/null
+++ b/test/files/run/t3368.check
@@ -0,0 +1,46 @@
+[[syntax trees at end of                    parser]] // newSource1.scala
+package <empty> {
+  abstract trait X extends scala.AnyRef {
+    def $init$() = {
+      ()
+    };
+    def x = {
+      val $buf = new _root_.scala.xml.NodeBuffer();
+      $buf.$amp$plus(new _root_.scala.xml.PCData("hi & bye"));
+      $buf.$amp$plus(new _root_.scala.xml.PCData("red & black"));
+      $buf
+    }
+  };
+  abstract trait Y extends scala.AnyRef {
+    def $init$() = {
+      ()
+    };
+    def y = {
+      {
+        new _root_.scala.xml.Elem(null, "a", _root_.scala.xml.Null, $scope, false, ({
+          val $buf = new _root_.scala.xml.NodeBuffer();
+          $buf.$amp$plus({
+            {
+              new _root_.scala.xml.Elem(null, "b", _root_.scala.xml.Null, $scope, true)
+            }
+          });
+          $buf.$amp$plus(new _root_.scala.xml.Text("starthi & bye"));
+          $buf.$amp$plus({
+            {
+              new _root_.scala.xml.Elem(null, "c", _root_.scala.xml.Null, $scope, true)
+            }
+          });
+          $buf.$amp$plus(new _root_.scala.xml.Text("world"));
+          $buf.$amp$plus({
+            {
+              new _root_.scala.xml.Elem(null, "d", _root_.scala.xml.Null, $scope, true)
+            }
+          });
+          $buf.$amp$plus(new _root_.scala.xml.Text("stuffred & black"));
+          $buf
+        }: _*))
+      }
+    }
+  }
+}
+
diff --git a/test/files/run/t3368.scala b/test/files/run/t3368.scala
new file mode 100644
index 0000000000..aaf34b43fb
--- /dev/null
+++ b/test/files/run/t3368.scala
@@ -0,0 +1,18 @@
+
+import scala.tools.partest.ParserTest
+
+
+object Test extends ParserTest {
+
+  override def code = """
+  trait X {
+    // error: in XML literal: name expected, but char '!' cannot start a name
+    def x = <![CDATA[hi & bye]]> <![CDATA[red & black]]>
+  }
+  trait Y {
+    def y = <a><b/>start<![CDATA[hi & bye]]><c/>world<d/>stuff<![CDATA[red & black]]></a>
+  }
+  """
+
+  override def extraSettings = s"${super.extraSettings} -Yxml:coalescing"
+}