org-manual: Fix last modification

* doc/org-manual.org (Results of Evaluation): Fix footnote reference.
Use regular quotes so smart quotes can kick in, rewrite "header arg"
to "header argument". Use present tense instead of future.

doc/org-manual.org

@@ -17175,7 +17175,7 @@ default behavior is to automatically determine the result type.
      If =file= is missing, Org generates the base name of the output
      file from the name of the code block, and its extension from the
      =file-ext= header argument.  In that case, both the name and the
-     extension are mandatory.[fn:150]
+     extension are mandatory[fn:150].
 
      #+begin_example
      ,#+name: circle
@@ -21384,12 +21384,13 @@ on outline paths, assuming they are unique.
 
 [fn:149] The file will be empty after this operation.
 
-[fn:150] Due to the way this header arg is implemented, it implies
-“:results file”.  Therefore if it is set for multiple blocks at once
-(by a subtree or buffer property for example), all blocks will be forced
-to produce file results.  This is seldom desired behavior, so it is
-recommended to set this header only on a per-block basis.  It is possible
-that this aspect of the implementation might change in the future.
+[fn:150] Due to the way this header argument is implemented, it
+implies ":results file".  Therefore if it is set for multiple blocks
+at once (by a subtree or buffer property for example), all blocks are
+forced to produce file results.  This is seldom desired behavior, so
+it is recommended to set this header only on a per-block basis.  It is
+possible that this aspect of the implementation might change in the
+future.
 
 
 * Local variables                                                  :noexport: