largefiles: call readstandin() with changectx itself instead of rev or node
readstandin() takes "node" argument to get changectx by "repo[node]".
There are some readstandin() invocations, which use ctx.node(),
ctx.rev(), or '.' as "node" argument above, even though corresponded
changectx object is already looked up on caller side.
This patch calls readstandin() with already known changectx itself, to
avoid meaningless re-construction of changectx (indirect case via
copytostore() is also included).
BTW, copytostore() uses "rev" argument only for readstandin()
invocation. Therefore, this patch also renames it to "revorctx" to
indicate that it can take not only revision ID or so but also
changectx, for readability.
Run Mercurial tests with Vagrant:
$ vagrant up
$ vagrant ssh -c ./run-tests.sh