images: add support for fast jpeg down-sampling.

The new package pkg/images/fastjpeg uses djpeg(1) to quickly
down-sample images at load time as described here:

  http://jpegclub.org/djpeg/

Add benchmark comparing std lib jpeg.Decode and fastjpeg.DecodeDownsample
with a factor of 1, 2, 4, and 8.
Benchmark resizes a 4000x4000 pixel JPEG to 128x128.

Refactor in pkg/images to make images.Decode a little more readable.

Change-Id: I571db1f3c3068f99da4a01ec84fd246ef098a18c
Fixed calls to formatting functions

Change-Id: I3ec2af85364674ac6f1a88cd12b6cb369d8e50e1
importer/foursquare: minor typo

Change-Id: Ic3c0d2f01ea0e6dc191500ed2856810e8c9581d6
Merge "Fixed calls to formatting functions"
Merge "images: add support for fast jpeg down-sampling."
devcam server --makethings

Only creates twitter things for now.

http://camlistore.org/issue/417

Change-Id: I05d548e012586279e165c01468524ceb055ff17b
importer/foursquare: make test data for devcam

http://camlistore.org/issue/417

Change-Id: I753ac91aae5bd876b28e4473e4cf00af460deb95
importer: wire run (context) HTTP client with host HTTP client

Killing two birds with one stone: we don't need to set it in devcam
anymore now.

Also switched to using the short form (run's one) everywhere, for
consistency.

Change-Id: I1e72ab99a07392c4970b1ed19b6e460ff422a24a
Merge "importer: wire run (context) HTTP client with host HTTP client"
wip picasa

Change-Id: If1a8771a863e1f7d0797ec5a8e50cd3573718c95