Capture stack traces via synthesized errors when required.

When captureError() is called without an Error object, synthesize
one so we can grab an approximate stack trace.

Author: rcoup

lib/client.js

@@ -110,10 +110,8 @@ _.captureException = function captureError(err, kwargs, cb) {
     if(!(err instanceof Error)) {
         // This handles when someone does:
         //   throw "something awesome";
-        // We just send the "Error" as a normal message
-        // since there is no way to compute a stack trace
-        // See: https://github.com/mattrobenolt/raven-node/issues/18
-        return this.captureMessage('Error: ' + err, kwargs, cb);
+        // We synthesize an Error here so we can extract a (rough) stack trace.
+        var err = new Error(err);
     }
 
     var self = this;

test/raven.client.js

@@ -190,14 +190,16 @@ describe('raven.Client', function(){
             client.captureError(new Error('wtf?'));
         });
 
-        it('should send a plain text "error" as a Message instead', function(done){
-            // See: https://github.com/mattrobenolt/raven-node/issues/18
-            var old = client.captureMessage;
-            client.captureMessage = function(message) {
-                // I'm also appending "Error: " to the beginning to help hint
-                message.should.equal('Error: wtf?');
+        it('should send a plain text "error" with a synthesized stack', function(done){
+            var old = client.send;
+            client.send = function(kwargs) {
+                client.send = old;
+
+                kwargs['message'].should.equal("Error: wtf?");
+                kwargs.should.have.property('sentry.interfaces.Stacktrace');
+                var stack = kwargs['sentry.interfaces.Stacktrace'];
+                stack.frames[0]['function'].should.equal('captureError');
                 done();
-                client.captureMessage = old;
             };
             client.captureError('wtf?');
         });