[tuples] comment changes

[Aldy Hernandez]

Small comment fixes I found while writing the gimple API document.

I also found an orphaned prototype which I removed.

Committed to branch.

	* gimple.h (gimple_cond_invert): Remove prototype.
	(update_stmt_if_modified): Fix typo in comment.
	* gimple.c (walk_gimple_asm): Fix typo in comment.

Index: gimple.c
===================================================================
--- gimple.c	(revision 132428)
+++ gimple.c	(working copy)
@@ -1126,7 +1126,7 @@ walk_gimple_asm (gimple stmt, walk_tree_
    in WI).  If WI is NULL, no state is kept during traversal.
    The callback CALLBACK_STMT is called.  If CALLBACK_STMT returns
    true, it means that the callback function has handled all the
-   operands of STMT and it is no necessary to walk STMT's operands.
+   operands of STMT and it is not necessary to walk STMT's operands.
 
    If CALLBACK_STMT is NULL or it returns false, CALLBACK_OP is called
    on each operand of STMT via walk_tree.  Additional parameters to
Index: gimple.h
===================================================================
--- gimple.h	(revision 132428)
+++ gimple.h	(working copy)
@@ -501,7 +501,6 @@ gimple gimple_build_assign_with_ops (enu
 gimple gimple_build_call_vec (tree, VEC(tree, gc) *);
 gimple gimple_build_call (tree, size_t, ...);
 gimple gimple_build_cond (enum tree_code, tree, tree, tree, tree);
-void gimple_cond_invert (gimple);
 gimple gimple_build_label (tree label);
 gimple gimple_build_goto (tree dest);
 gimple gimple_build_nop (void);
@@ -893,7 +892,7 @@ update_stmt (gimple s)
     }
 }
 
-/* Update statement T if it has been optimized.  */
+/* Update statement S if it has been optimized.  */
 
 static inline void
 update_stmt_if_modified (gimple s)