c++: trailing end-of-lines in %parse-param

* src/parse-gram.y (add_param): No only skip ' ' and '\t', skip all
leading and trailing spaces.
* tests/regression.at (Lex and parse params): Check it.
* NEWS: Document it.

src/parse-gram.y

@@ -734,11 +734,13 @@ add_param (char const *type, char *decl, location loc)
 
   /* Strip the surrounding '{' and '}', and any blanks just inside
      the braces.  */
-  while (*--p == ' ' || *p == '\t')
-    continue;
+  --p;
+  while (isspace ((unsigned char) *p))
+    --p;
   p[1] = '\0';
-  while (*++decl == ' ' || *decl == '\t')
-    continue;
+  ++decl;
+  while (isspace ((unsigned char) *decl))
+    ++decl;
 
   if (! name_start)
     complain_at (loc, _("missing identifier in parameter declaration"));