dagparser: transplant part of 4e804302d30c

check-code: catch "echo -n" in tests

test-init: replace 'echo -n' with 'printf' The '-n' argument to echo is a non-standard extension that isn't supported on Mac OS X 10.6.

revset: fix outgoing argument handling

debugbuilddag: escape backslash properly in help string

url.py: removed 'file' inheritance in the httpsendfile class Since py3k doesn't have a "file" builtin and, consequently, doesn't support inheriting from it, this patch refactors the httpsendfile class to wrap the objects returned by the builtin "open" function while adding the necessary methods (__len__ for constructing the Content-Length header and read, write, close and seek for the file-like interface).