Checks if 'command' can be found either in path
        or is a full name to an existing file.

def check_tool_aux(command):
    """ Checks if 'command' can be found either in path
        or is a full name to an existing file.
    """
    assert isinstance(command, basestring)
    dirname = os.path.dirname(command)
    if dirname:
        if os.path.exists(command):
            return command
        # Both NT and Cygwin will run .exe files by their unqualified names.
        elif on_windows() and os.path.exists(command + '.exe'):
            return command
        # Only NT will run .bat files by their unqualified names.
        elif os_name() == 'NT' and os.path.exists(command + '.bat'):
            return command
    else:
        paths = path.programs_path()
        if path.glob(paths, [command]):
            return command