Start a program in a subprocess. Return the process object for it.
Similar to `start-process', but may invoke a file handler based on
`default-directory'. See Info node `(elisp)Magic File Names'.
This handler ought to run PROGRAM, perhaps on the local host,
perhaps on a remote host that corresponds to `default-directory'.
In the latter case, the local part of `default-directory' becomes
the working directory of the process.
PROGRAM and PROGRAM-ARGS might be file names. They are not
objects of file handler invocation. File handlers might not
support pty association, if PROGRAM is nil.