from my examination of the tahoe_fuse ('impl_a') code, it looks like
the intention is to cache the file contents in memory while it's open,
since it does in fact do that. however it looks like it also ignored
that cache entirely, and made an individual tahoe webapi GET request
for each and every read() operation regardless of the relative size of
the read block and the file in question.
this changes that to make read() use the data in memory rather than
fetch the data over again. if there's something more subtle going
on, please let me know.
specifically change the expectation of the code to be such that the node-url
(self.url) always includes the trailing slash to be a correctly formed url
moreover read the node-url from the 'node.url' file found in the node 'basedir'
and only if that doesn't exist, then fall back to reading the 'webport' file
from therein and assuming localhost. This then supports the general tahoe
pattern that tools needing only a webapi server can be pointed at a directory
containing the node.url file, which can optionally point to another server,
rather than requiring a complete node dir and locally running node instance.
