Fix a couple oversights:
* correctly parse max_retries from args
* use the right variable name in curating FTP
Demo for E. coli
Allow a gateway to request that its own certificate version be included
in the certificate manifest.  This is to allow non-writer gateways to
get their cert and closure information.
Allow a pending download to be cancelled.
Remove gratuitous debugging information
Set an upper bound of 10 HTTP 302s to process at once.  Also, add the
necessary code to get the gateway's cert version information in the
certificate manifest.
Demo GenBank dataset
Remove ODBC requirement from INSTALL
Remove on-disk AG caching for dataset status.
Add quickstart handling code in AG startup.  Also, remove commented-out
code from earlier.
AG curl driver: correctly report the number of bytes transferred, so we
can infer an EOF.  Interpret a bad file range as EOF.
Have the AG HTTP server infer EOF if the driver doesn't give back a full
block.  Send the partial block with the driver-reported size.
Clean up the coherency model in the AG.  The AG's map-info stores cached data
from the MS, from the driver, and from the specfile.  Add methods to
explicitly deal with each kind of cached data.  Also, more bugfixes
along the way with more testing.
Correctly generate the FTP URL when generating an FTP-based specfile.
Refactored open() implementation to clean it up, and to allow opening an
existing file to retry manifest downloads when the path itself becomes
stale.
More robust manifest revalidation code.
More robust clean-up code for file handle destruction.
WIP: read() clean-up.  Fix some bugs when dealing with the AG.  Still a
WIP since there are still some memory leaks, and the file (from the AG)
can have trailing zeros.
Better manifest-download documentation.  Differentiate between stale
path metadata and stale gateway metadata.