Support CTFE exception handling

Just exposes the constructors for Exception and Error, so that they are
CTFEable.

import/object.di

@@ -321,15 +321,31 @@ class Throwable : Object
 
 class Exception : Throwable
 {
-    this(string msg, string file = __FILE__, size_t line = __LINE__, Throwable next = null);
-    this(string msg, Throwable next, string file = __FILE__, size_t line = __LINE__);
+    this(string msg, string file = __FILE__, size_t line = __LINE__, Throwable next = null)
+    {
+        super(msg, file, line, next);
+    }
+
+    this(string msg, Throwable next, string file = __FILE__, size_t line = __LINE__)
+    {
+        super(msg, file, line, next);
+    }
 }
 
 
 class Error : Throwable
 {
-    this(string msg, Throwable next = null);
-    this(string msg, string file, size_t line, Throwable next = null);
+    this(string msg, Throwable next = null)
+    {
+        super(msg, next);
+        bypassedException = null;
+    }
+
+    this(string msg, string file, size_t line, Throwable next = null)
+    {
+        super(msg, file, line, next);
+        bypassedException = null;
+    }
     Throwable   bypassedException;
 }