largefiles: updatelfiles should use working dir standins, not standins from p1 This makes a difference when working directory is dirty, especially when merging with a revision for which we don't have largefiles.

largefiles: simplify cachelfiles - don't spend a lot of time checking hashes cachelfiles jumped through loops to handle merges and modified files ... but it did apparently no longer have a valid reason to do so. It should just always make sure that the largefiles referenced from the standins are present - no matter which actual largefile is stored in the working directory. If there is no standin then there is nothing to fetch. The old code usually verified the hash of all largefiles every time this function was invoked - for examply by 'update'. This change makes a trivial noop update 5-10 seconds faster on our repo (with the other 50% spent doing another unnecessary hashing of all largefiles).