bug#51010: 29.0.50; python completion breaks upon non-trivial rl config

[Carlos Pita]

(originally reported in https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25753)

Using this readline config:

> cat .inputrc

set completion-ignore-case on
set completion-display-width 80
set completion-prefix-display-length 5
set show-all-if-ambiguous on
set skip-completed-text on
set colored-stats on
set blink-matching-paren on
set menu-complete-display-prefix on

native completions received by python.el look like:

    0__dummy_completion__ [0m [K  1__dummy_completion__ [0m [K

which wreaks havoc with the native completion mechanism.

This mechanism is quite fragile and already complex enough, I don't
feel like approaching the issue on a case by case basis and always
catching up with upstream and with configuration combinatorics.

One alternative is to set the INPUTRC environment variable in order to
reset the user config. Short of doing that, we could just make one
regex less strict:

                  (comint-redirect-finished-regexp
                   "1__dummy_completion__[[:space:]]*\n")

to:
                  (comint-redirect-finished-regexp
                   "1__dummy_completion__.*\n")

I propose this minimal change. A priori I'd expect that the text
"1__dummy_completion__" will always be in the output, no matter the
specific configuration, although the fact that python.el is already
doing `set show-all-if-ambiguous on` is a testimony to how fallible my
expectations are.

Best regards,
Carlos