Style fixups.

Docs/Manual_style_guidelines.txt:
  Add item on operators.
Docs/manual.texi:
  Style fixup to changelog.

Docs/Manual_style_guidelines.txt

@@ -261,3 +261,5 @@ It's "unstable", not "instable". ;-)
 
 It's "full-text", not "fulltext".
 
+Logical NOT/OR/AND are operators, not functions, so they take operands, not arguments.
+

Docs/manual.texi

@@ -49680,7 +49680,7 @@ not yet 100% confident in this code.
 @node News-3.23.51, News-3.23.50, News-3.23.x, News-3.23.x
 @appendixsubsec Changes in release 3.23.51
 @itemize @bullet
-Fixed the result from @code{IF()} to be case insensitive if the second and
+Fixed the result from @code{IF()} to be case-insensitive if the second and
 third arguments are case-sensitive.
 @end itemize