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
context: minor typos in documentation.

Learned that cancelled is appropriate for non-US English, but the function is
IsCanceled, so I went with consistency.

Change-Id: If63a8af75338780c2f8e81bf4404fc4b5f852d77
test/transport.go: move to httputil, so we can use it without linking testing

Change-Id: I889d167a78ef0fba5ef2e9e3e884f594e151e940
images: fix broken test

Exif.DateTime now always returns a time.Local location when zone is unknown.

Change-Id: I898516398a88bc8dcd8daf26f87c801a24cc1d7a
Merge "test/transport.go: move to httputil, so we can use it without linking testing"
importer/twitter: add TestDataMaker to generate imported tweets

Also fix first user_timeline call (no maxId).

http://camlistore.org/issue/417

Change-Id: I1157331bd876a6400e16d0fd18712d8c459fdc20
Merge "context: minor typos in documentation."
pkg/sorted/buffer: flesh out, add test

Change-Id: I18f57425ad2e9a4d692d4efe865fea81e8f143e3
Merge "pkg/sorted/buffer: flesh out, add test"
fs: handle directory permanode titles

Set corresponding permanode title on new root,
new directory and directory rename.

Change-Id: I5432e14ef57d6c0c5555b11e895e8b8ad6d8efcf
make: run 'devcam test' for presubmit target

The previous behavior (now build target oldpresubmit) was slightly different
than devcam test; it didn't copy files to a clean directory and test in
isolation.  The buildbot uses devcam test, and for consistency 'make
presubmit' should too.

This runs devcam test with -short, mirroring -short from the previous
presubmit.  The buildbot runs devcam without -short.

Change-Id: I71e308bd16104004a8cd790901e88edebedab2a9
Merge "make: run 'devcam test' for presubmit target"
Merge "fs: handle directory permanode titles"
picasa importer: remove Run-private HTTPClient

A more complete version of Aaron Boodman's
https://camlistore-review.googlesource.com/#/c/3066/
in removing Transports. As Aaron pointed out,
(https://groups.google.com/d/msg/camlistore/9OwQKH6z7rY/840oQrRgsGIJ) it
is illegal for oauth.Transport.Transport to ever be another instance of
oauth.Transport.

So this commit tries hard to use Context's HTTPClient
everywhere and make sure to have its Transport an *oauth.Transport, but
that's Transport is not an *oauth.Transport, but the underlying
Transport.

To eliminate "403: Token not found" errors, we set
oauth.Config.AccessType, oauth.Config.ApprovalPrompt to
"offline", "force".
This rewards us with a non-empty Token.RefreshToken,
and store the full Token in AcctAttrOAuthToken.
This enables us to import continuously without user intervention.

Change-Id: I4defb346abfcf3f6c17597fc2dc23a6e536eda37
dockertest: skip test when DB in container not ready

http://camlistore.org/issue/474

Change-Id: Id65b3c35a2f38466c4d7370bad4c5f73a8cb22db
Merge "dockertest: skip test when DB in container not ready"
Merge "picasa importer: remove Run-private HTTPClient"
Fixed calls to formatting functions

Change-Id: I3ec2af85364674ac6f1a88cd12b6cb369d8e50e1
importer/foursquare: minor typo

Change-Id: Ic3c0d2f01ea0e6dc191500ed2856810e8c9581d6
Merge "Fixed calls to formatting functions"