Ok, I think I have something clean.
(btw, I'm done with the copyleft paperwork)

Here is the diff, and a potential log message.

Jean-Christophe 


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Add optional regexp for subr-x.el trimming functions

* lisp/emacs-lisp/subr-x.el (string-trim-left) (string-trim-right) (string-trim): add optional regexp that defaults on the original behavior.
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