REPL prompt is stored as current input when navigating input history

[oyvindstegard]

This applies at least to Emacs 25, I do not know about earlier versions.
0. Start clean Emacs instance with emacs -Q, load up required libs, inf-clojure, clojure-mode...

1. Start REPL with M-x inf-clojure
2. Input something and evaluate with RET
3. Describe variable comint-stored-incomplete-input, which should have the value nil, all OK so far.
4. Without inputting anything new, navigate to previous history item with M-p
5. Describe variable comint-stored-incomplete-input again, and now it contains the actual prompt with fontification and all:
   #("user=> " 0 7 ....)
6. Try going back to current input with M-n, and the prompt gets inserted as actual "restored incomplete input", which is clearly wrong. So you end up with "user=> user=> ". This causes even bigger problems when using the default read-only-prompt setting (navigating history stops working properly).

[oyvindstegard]

Tried to fix it with the following commit:
oyvindstegard@ac08fdd

[bbatsov]

Seems like a reasonable fix. You should have filed a PR.