Speedups

[pjrobertson]

I meant to mention this on #1180 but forgot… so I've done it myself.

I wasn't too fond of the mutableCopy that was done when populating the 3rd pane for 'open with…', just because mustableCopies are wasteful.

In this commit I've avoided it like the plague and done what I think is a little neater.

Here's the stats:

Rob's way:

2012-11-13 09:31:00.470 Quicksilver[17859:303] Time: 3.082813
2012-11-13 09:31:06.725 Quicksilver[17859:303] Time: 3.066322
2012-11-13 09:31:12.398 Quicksilver[17859:303] Time: 3.067382
2012-11-13 09:31:17.980 Quicksilver[17859:303] Time: 3.105199
2012-11-13 09:31:23.366 Quicksilver[17859:303] Time: 3.051625
Sum = 18.5696
Avg = 3.0949

My way:

2012-11-13 09:31:46.183 Quicksilver[18048:303] Time: 2.888232
2012-11-13 09:31:52.231 Quicksilver[18048:303] Time: 2.790452
2012-11-13 09:31:57.658 Quicksilver[18048:303] Time: 2.745043
2012-11-13 09:32:03.093 Quicksilver[18048:303] Time: 2.796696
2012-11-13 09:32:08.252 Quicksilver[18048:303] Time: 2.771102
2012-11-13 09:32:13.054 Quicksilver[18048:303] Time: 2.741780
2012-11-13 09:32:18.048 Quicksilver[18048:303] Time: 2.751693
2012-11-13 09:32:22.767 Quicksilver[18048:303] Time: 2.742932
2012-11-13 09:32:28.189 Quicksilver[18048:303] Time: 2.981644
Sum = 25.2096
Avg = 2.8011

Diff = 9.5% improvement ```

If everyone (mainly @skurfer) is happy with this, I'll squash these two commits and then do the same for the copy to.../move to… actions.
I've left the profiling code in in the 1st commit incase anybody wants to test it on their machine :)

[pjrobertson]

Oh yeah, and I removed objectsAtIndexes: from the NSArray category, since that's now defined by the OS and we don't want to override it :)

…I've removed it even though the two methods may be identical (?), but I think our code is slightly faster. Like 1% faster...