largefiles: refactoring - create destination dir in lfutil.link
largefiles: refactoring - return hex from _getfile and copyandhash
largefiles: refactoring - use findfile in localstore._getfile
largefiles: drop lfutil.blockstream - use filechunkiter like everybody else

The old chunk size is kept - just to avoid changing it.
largefiles: remove blecch from lfutil.copyandhash - don't close the passed fd
largefiles: don't close the fd passed to store._getfile
largefiles: move protocol conversion into getlfile and make it an iterable

Avoid the intermediate limitreader and filechunkiter between getlfile and
copyandhash - return the right protocol and put the complexity where it better
can be managed.
largefiles: drop limitreader, use filechunkiter limit

filechunkiter.close was a noop.
largefiles: getlfile must hit end of HTTP chunked streams to reuse connections

We did read the exactly the right number of bytes from the response body. But
if the response came in chunked encoding then that meant that the HTTP layer
still hadn't read the last 0-sized chunk and expected the app layer to read
more data from the stream. The app layer was however happy and sent another
request which had to be sent on another HTTP connection while the old one was
lingering until some other event closed the connection.

Adding an extra read where we expect to hit the end of file makes the HTTP
connection ready for reuse. This thus plugs a real socket leak.

To distinguish HTTP from SSH we look at self's class, just like it is done in
putlfile.
largefiles: 'put' should store 'source' file in under 'hash', also in localstore
largefiles: stat all largefiles in one batch before downloading

This avoids a lot of expensive roundtrips to remote repositories ... but might
be slightly slower for local operations.

This will also change some aborts on missing files to warnings. That will in
some situations make it possible to continue working on a repository with
missing largefiles.
largefiles: use filechunkiter for iterating largefile when serving getlfile

The default file iterator is line based and will give odd chunk sizes - often
very short and relatively expensive.
largefiles: don't hash all largefiles when initializing a lfdirstate

The largefiles will be hashed on demand if necessary ... and sometimes it isn't
necessary.
dispatch: print 'abort:' when a pre-command hook fails (BC)

This also changes the exit code from whatever the hook returned to 255. This
brings it in line with all the other hooks that abort.