Fix make maintainer-clean with queryjumblefuncs.*.c files in src/backend/nodes/

The files generated by gen_node_support.pl for query jumbling
(queryjumblefuncs.funcs.c and queryjumblefuncs.switch.c) were not being
removed on make maintainer-clean (they need to remain around after a
simple "clean").  This commit makes the operation consistent with the
copy, equal, out and read files.

While on it, update a comment in the nodes'README where a reference to
queryjumblefuncs.funcs.c was missing.

Reported-by: Nathan Bossart
Reviewed-by: Richard Guo, Daniel Gustafsson
Discussion: https://postgr.es/m/ZBgAfTHcL6W7zGdW@paquier.xyz

src/backend/nodes/Makefile

@@ -95,7 +95,8 @@ $(top_builddir)/src/include/nodes/header-stamp: node-support-stamp
 copyfuncs.o: copyfuncs.c copyfuncs.funcs.c copyfuncs.switch.c | node-support-stamp
 equalfuncs.o: equalfuncs.c equalfuncs.funcs.c equalfuncs.switch.c | node-support-stamp
 outfuncs.o: outfuncs.c outfuncs.funcs.c outfuncs.switch.c | node-support-stamp
+queryjumblefuncs.o: queryjumblefuncs.c queryjumblefuncs.funcs.c queryjumblefuncs.switch.c | node-support-stamp
 readfuncs.o:  readfuncs.c readfuncs.funcs.c readfuncs.switch.c | node-support-stamp
 
 maintainer-clean: clean
-	rm -f node-support-stamp $(addsuffix funcs.funcs.c,copy equal out read) $(addsuffix funcs.switch.c,copy equal out read) nodetags.h
+	rm -f node-support-stamp $(addsuffix funcs.funcs.c,copy equal out queryjumble read) $(addsuffix funcs.switch.c,copy equal out queryjumble read) nodetags.h

src/backend/nodes/README

@@ -88,10 +88,10 @@ Suppose you want to define a node Foo:
    If you intend to inherit from, say a Plan node, put Plan as the first field
    of your struct definition.  (The T_Foo tag is created automatically.)
 2. Check that the generated support functions in copyfuncs.funcs.c,
-   equalfuncs.funcs.c, outfuncs.funcs.c and readfuncs.funcs.c look
+   equalfuncs.funcs.c, outfuncs.funcs.c, queryjumblefuncs.funcs.c and
-   correct.  Add attributes as necessary to control the outcome.  (For
+   readfuncs.funcs.c look correct.  Add attributes as necessary to control the
-   some classes of node types, you don't need all four support functions.
+   outcome.  (For some classes of node types, you don't need all the support
-   Use node attributes similar to those of related node types.)
+   functions.  Use node attributes similar to those of related node types.)
 3. Add cases to the functions in nodeFuncs.c as needed.  There are many
    other places you'll probably also need to teach about your new node
    type.  Best bet is to grep for references to one or two similar existing