largefiles: omit redundant isstandin() before splitstandin() There are many isstandin() invocations before splitstandin(). The former examines whether specified path starts with ".hglf/". The latter returns after ".hglf/" of specified path if it starts with that prefix, or returns None otherwise. Therefore, value returned by splitstandin() can be used for replacement of preceding isstandin(), and this replacement can omit redundant string comparison after isstandin().

misc: update descriptions about removed file for filectxfn Since 650b5b6e75ed, filectxfn for memctx should return None for removed file instead of raising IOError.