Reverted recent changes to constructors for Throwable and Error.

The changes to the other exception types remain, but apparently having
default file and line numbers on Throwable and Error causes some
problems with low-level stuff. And as Don points out, they really should
be abstract anyway, so the default arguments don't matter much anyay.
However, apparently, some changes have to be made to the compiler before
that can happen. So, for now, just the default arguments are fixed.

import/object.di

@@ -323,8 +323,8 @@ class Exception : Throwable
 
 class Error : Throwable
 {
-    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);
+    this(string msg, Throwable next = null);
+    this(string msg, string file, size_t line, Throwable next = null);
     Throwable   bypassedException;
 }
 

src/object_.d

@@ -1364,13 +1364,13 @@ unittest
 
 class Error : Throwable
 {
-    this(string msg, Throwable next, string file = __FILE__, size_t line = __LINE__)
+    this(string msg, Throwable next = null)
     {
-        super(msg, file, line, next);
+        super(msg, next);
         bypassedException = null;
     }
 
-    this(string msg, string file = __FILE__, size_t line = __LINE__, Throwable next = null)
+    this(string msg, string file, size_t line, Throwable next = null)
     {
         super(msg, file, line, next);
         bypassedException = null;
@@ -1385,17 +1385,17 @@ unittest
 {
     {
         auto e = new Error("msg");
-        assert(e.file == __FILE__);
-        assert(e.line == __LINE__ - 2);
+        assert(e.file is null);
+        assert(e.line == 0);
         assert(e.next is null);
         assert(e.msg == "msg");
         assert(e.bypassedException is null);
     }
 
     {
-        auto e = new Error("msg", new Exception("It's an Excepton!"), "hello", 42);
-        assert(e.file == "hello");
-        assert(e.line == 42);
+        auto e = new Error("msg", new Exception("It's an Excepton!"));
+        assert(e.file is null);
+        assert(e.line == 0);
         assert(e.next !is null);
         assert(e.msg == "msg");
         assert(e.bypassedException is null);