Incorporate the UG's cache and url handlers into libsyndicate, since the
AG will make use of both.  TODO: refactor the UG's cache and url
handlers to use libsyndicate's.
Add 302 response message
Don't include log.h in the UG cache.
Remove ag_driver from md_syndicate_conf.
Have md_syndicate_conf store the volume ID, obtained from the ms_client
Remove commented-out uploader thread, which is no longer used in
ms-client.h
Remove #include for the UG manifest in its url handler.
Make cache soft and hard limits in the UG part of the UG_opts structure,
not the md_syndicate_conf structure.
Add md_{read,write,send,recv}_uninterrputed() methods to
libsyndicate/util.cpp.  Remove unused signal handler code.
For now, retire the AG SQL driver.  We can effectively use the psql (or
equivalent) binaries in the shell driver to access databases.  Revisit
the sql driver at a later time, but for now it isn't compatible with the
current AG architecture.
Forgot to add the AG's driver and http logic
Get a README.md going for AG drivers.
WIP (needs testing): AG HTTP/FTP driver
Add build target for AG HTTP/FTP driver
Have the AG use libsyndicate's disk cache implementation (refactored and
reincorporated from the UG).  The AG will store blocks obtained from the
driver, as well as manifest-related metadata, so it can avoid querying
the driver for information more than once over the course of the file's
lifetime.
Bring the AG disk and shell drivers up to speed with minor changes to
the AG driver model.
Bugfixes to the AG, as well as new features, in light of testing.
* Have the AG cache blocks and stats for files.
* Fix memory leak from downloading the AG's filesystem mapping from the
MS.
Move test-sql.xml to tests/legacy/, since it's for a legacy driver.
Add a simple specfile for the AG HTTP/FTP driver (test-curl.xml)