httputil: allow full error serving when with devcam

When hacking on e.g. importers, I sometimes want to use devcam with
-hostname, to test with a non local context. In which case, when hitting
an error httputil.ServeError would not print the full error, which
makes it harder to debug.

Change-Id: I2fb8c97748d4f077404fbf12010addd6e7af3572
pkg/blobserver: Modify the definition of the BlobStreamer interface.

Code implementing this interface will use NewBlob(), which has been
modified to return a pointer to blob.Blob. So change the StreamBlobs
function in this interface to also send *.blob.Blob

Change-Id: Ia3b94c3f41f95cb31e96762d4c39b3172cc978f2
twitter importer: fixed to new API

Change-Id: I490001a1f780f1074baa78a4daa563e55096242c
Merge "httputil: allow full error serving when with devcam"
Merge "twitter importer: fixed to new API"
importer/twitter: little fixes

Change-Id: I11ee5c6c5779c5e479120653f4131c0b4edfb2c8
Rewrite Picasa importer for the new Importer API

Reorganizes some common things with Foursquare.

Needs thorough review: several FIXMEs and TODOS included!

Change-Id: I0789f4732412aa559078ec2c6b6797925ab8cd05