Doctest as guild script

[KAction]

Here is patch (I wrote about it two weeks ago or so).

During moving to guild I found one more limitation --- if called
in REPL, (doctest "(foo)") do not restore previous state of
interpreter. I am going to improve it and continuation master's
advice is welcome.

Another issue is license. I did not signed paper about Guile 
(unfortunately, it is impossible to sign paper for all GNU
project at once). Is it critical for such non-essensial part of
Guile?

Best regards