Fix exception output for module load exceptions

So instead of:

node.js:201
        throw e; // process.nextTick error, or 'error' event on first tick
              ^

You will now see:

path/to/foo.js:1
throw new Error('bar');
      ^

This is a sub-set of isaacs patch here:

https://github.com/joyent/node/issues/3235

The difference is that this patch purely adresses the exception output,
but does not try to make any behavior changes / improvements.

lib/module.js

@@ -304,11 +304,16 @@ Module._load = function(request, parent, isMain) {
   }
 
   Module._cache[filename] = module;
+
+  var hadException = true;
+
   try {
     module.load(filename);
-  } catch (err) {
+    hadException = false;
-    delete Module._cache[filename];
+  } finally {
-    throw err;
+    if (hadException) {
+      delete Module._cache[filename];
+    }
   }
 
   return module.exports;

test/message/stack_overflow.out

@@ -1,6 +1,6 @@
 before
 
-module.js:311
+*test*message*stack_overflow.js:31
-    throw err;
+function stackOverflow() {
-          ^
+                      ^
 RangeError: Maximum call stack size exceeded

test/message/throw_custom_error.out

@@ -1,6 +1,6 @@
 before
 
-module.js:311
+*test*message*throw_custom_error.js:31
-    throw err;
+throw { name: 'MyCustomError', message: 'This is a custom message' };
-          ^
+^
 MyCustomError: This is a custom message

test/message/throw_non_error.out

@@ -1,6 +1,6 @@
 before
 
-module.js:311
+*/test/message/throw_non_error.js:31
-    throw err;
+throw { foo: 'bar' };
-          ^
+^
 [object Object]

test/message/undefined_reference_in_new_context.out

@@ -1,8 +1,8 @@
 before
 
-module.js:311
+*test*message*undefined_reference_in_new_context.js:34
-    throw err;
+script.runInNewContext();
-          ^
+       ^
 ReferenceError: foo is not defined
     at evalmachine.<anonymous>:*
     at Object.<anonymous> (*test*message*undefined_reference_in_new_context.js:*)