Spelling fixes

* doc/misc/calc.texi (Predefined Units): Use the bland modern
scientific style for spelling the units “ampere” and
“angstrom” rather than the older style “Ampere” and
“Ångstrom”.  The latter spelling was wrong anyway (it should
have been “Ångström”).
* lisp/emacs-lisp/ert.el (ert--explain-equal-rec):
Fix misspelling of ‘atom’ in code.

lisp/emacs-lisp/ert.el

@@ -515,7 +515,7 @@ Returns nil if they are."
                   for xi = (ert--explain-equal-rec ai bi)
                   do (when xi (cl-return `(array-elt ,i ,xi)))
                   finally (cl-assert (equal a b) t))))
-      ((pred atomp)
+      ((pred atom)
        (if (not (equal a b))
            (if (and (symbolp a) (symbolp b) (string= a b))
                `(different-symbols-with-the-same-name ,a ,b)