Shell invoked via shell-file-name

[Christoph Scholtes <cschol2112@googlemail.com>]

Is there a way to invoke a shell via `shell-file-name' with additional
command line parameters?

I am trying to use cygwin for certain things on a Windows system, for
example mercurial, ruby or ack. Ruby works fine since there is an
executable (*.exe) that Emacs finds on the exec-path (or PATH) and
executes, but mercurial (hg) is just a Python script and ack just a Perl
script. They need the shell to invoke the correct interpreter.

I can call, for example, ack correctly from Windows cmd.exe like this:

  C:\>cywgin\bin\bash -l -c ack

whereas

  C:\>cygwin\bin\bash -c ack

does not work

  cygwin/bin/bash: ack: command not found

`shell-command-switch' allows to specify the `-c' option, but there is
no way to specify the `-l' or `--login', is there?

Christoph