Copy buffer bytes

[bill-rich]

buffer.Bytes() gives a pointer to the slice that is being reused. Need to copy the slice to avoid weirdness later.

[dustin-decker]

Preallocating the slice and using copy would be better here

https://gist.github.com/xogeny/b819af6a0cf8ba1caaef

[trufflesteeeve]

Based on runs of the metrics, it seems like whatever you do, either copy or append, is good so long as you preallocate the destination slice.

[bill-rich]

I thought pre-allocating should be the fastest too. For some reason in this case append seems to be slightly faster.

With append on my test repo:
32.593306s - 32.818896 seconds

With make and copy:
32.906427 - 33.12590 seconds

Not a huge difference, but I've been getting those results consistently. I'll merge as is for now to get things fixed and run some tests against a really large repo to see how the two compare.

[dustin-decker]

There are probably some external variables there, the clean benchmarks show that pre-allocation with either append or copy is faster.