Emacs python-mode docstring fill bug. Emacs fills the 1st line of a docstring incorrectly. The fill width is counted from the """, where for the rest of the lines, the fill is counted from the beginning of the line. See bugs https://debbugs.gnu.org/cgi/bugreport.cgi?bug=20860 and https://debbugs.gnu.org/cgi/bugreport.cgi?bug=21254

test.py

# -*- fill-column: 40; -*-
def f():
    """a a a a a a a a a a a a a a a a a a a
    a a a a a a a a a a a a a a a a a a
    a a a a a
    """
    def f():
        """a a a a a a a a a a a a a a a a a a a
        a a a a a a a a a a a a a a a a
        a a a a a a a
        """
        def f():
            """a a a a a a a a a a a a a a a a a a a
            a a a a a a a a a a a a a a
            a a a a a a a a a
            """
            #                           ↑
            #                   column 40