mu4e: make mu4e~read-char-choice case-insensitive

Make mu4e~read-char-choice case insensitive if there is no exact
match. Small convenience.

NEWS.org

@@ -17,6 +17,9 @@
    - Make `shr' the default renderer for rich-text emails
    - Allow for resending existing messages, possibly editing them. M-x
      mu4e-compose-resend, or use the menu; no shortcut.
+   - Let `mu4e~read-char-choice' become case-insensitive if there is
+     no exact match; small convenience that affects most the
+     single-char option reading in mu4e.
              
 ** 0.9.16
 

mu4e/mu4e-utils.el

@@ -228,14 +228,18 @@ Does a local-exit and does not return. In emacs versions below
   (user-error "%s" (apply 'mu4e-format frm args)))
 
 (defun mu4e~read-char-choice (prompt choices)
-  "Compatiblity wrapper for `read-char-choice'.
-That function is available which emacs-24 only."
-  (let ((choice) (ok) (inhibit-quit nil))
-    (while (not ok)
+  "Read and return one of CHOICES, prompting for PROMPT.
+Any input that is not one of CHOICES is ignored. This mu4e's
+version of `read-char-choice', that becomes case-insentive after
+trying an exact match."
+  (let ((choice) (chosen) (inhibit-quit nil))
+    (while (not chosen)
       (message nil);; this seems needed...
       (setq choice (read-char-exclusive prompt))
-      (setq ok (member choice choices)))
-    choice))
+      (setq chosen (or (member choice choices)
+		     (member (downcase choice) choices)
+		     (member (upcase choice) choices))))
+    (car chosen)))
 
 (defun mu4e-read-option (prompt options)
   "Ask user for an option from a list on the input area.