fix(reporter/base): don't assume error message is first line of stack

The current implementation assumes that the first line of the err.stack
is the error message. This is not the case for Safari. When using Mocha
with a different HTML generator (e.g. Consolify) this produces weirdly
formatted output with no error message.

lib/reporters/base.js

@@ -168,11 +168,18 @@ exports.list = function(failures){
     var err = test.err
       , message = err.message || ''
       , stack = err.stack || message
-      , index = stack.indexOf(message) + message.length
-      , msg = stack.slice(0, index)
+      , index = stack.indexOf(message)
       , actual = err.actual
       , expected = err.expected
       , escape = true;
+    if (index === -1) {
+      msg = message;
+    } else {
+      index += message.length;
+      msg = stack.slice(0, index);
+      // remove msg from stack
+      stack = stack.slice(index + 1);
+    }
 
     // uncaught
     if (err.uncaught) {
@@ -198,9 +205,8 @@ exports.list = function(failures){
       }
     }
 
-    // indent stack trace without msg
-    stack = stack.slice(index ? index + 1 : index)
-      .replace(/^/gm, '  ');
+    // indent stack trace
+    stack = stack.replace(/^/gm, '  ');
 
     console.log(fmt, (i + 1), test.fullTitle(), msg, stack);
   });

test/reporters/base.js

@@ -110,4 +110,32 @@ describe('Base reporter', function () {
     errOut.should.match(/expected/);
   });
 
+  it('should remove message from stack', function () {
+    var err = {
+      message: 'Error',
+      stack: 'Error\nfoo\nbar',
+      showDiff: false
+    };
+    var test = makeTest(err);
+
+    Base.list([test]);
+
+    var errOut = stdout.join('\n').trim();
+    errOut.should.equal('1) test title:\n     Error\n  foo\n  bar')
+  });
+
+  it('should not modify stack if it does not contain message', function () {
+    var err = {
+      message: 'Error',
+      stack: 'foo\nbar',
+      showDiff: false
+    };
+    var test = makeTest(err);
+
+    Base.list([test]);
+
+    var errOut = stdout.join('\n').trim();
+    errOut.should.equal('1) test title:\n     Error\n  foo\n  bar')
+  });
+
 });