Make various popular storage targets be Stringers. Optional, for upcoming sync handler rewrite.

Change-Id: I8cc961ace8b6093b1dbd82bc39ba3fc334f1d5c7
s3: be a Stringer, make default host more explicit, add failure injection

Change-Id: I1c24e97ef4b901e3be62fbb7e34c3f53787eedb1
doc: add CAMLI_S3_FAIL_PERCENT var

Change-Id: Ie2c85da2bfeefc9e5ae98c14c5d879d7208a82f1
Merge branch 'master' of https://camlistore.googlesource.com/camlistore
Rewritten sync handler.

Fix deadlock, much better status page, show per-blob status & errors,
clear errors when they've resolved themselves, fix known data race.

Change-Id: I968de0de4f308ff0a410adceb181a0712800d401