Optimize chkPS

Use EXX instead of the stack for HL protection and remove all
spurious uses of chkPS,

I wanted to inline chkPS in next because of its "tight loop" status,
but for reasons I don't understand, doing so breaks Collapse OS.
Later...

blk/285

@@ -1,11 +1,11 @@
 CODE (?br)           ( 0x67 )
-    HL POPqq, chkPS,
+    HL POPqq,
     HLZ,
     JRZ, L2 BWR ( BR + 2. False, branch )
     L1 BSET ( loop will jump here )
     ( True, skip next 2 bytes and don't branch )
     IY INCss, IY INCss,
-    JPNEXT,
+    JPNEXT, NOP, NOP, NOP,
 CODE (loop) ( 0x77 )
     0 IX+ INC(IXY+), IFZ, 1 IX+ INC(IXY+), THEN, ( I++ )
     ( Jump if I <> I' )

blk/286

@@ -1,11 +1,11 @@
 CODE >R ( 0xa8 )
-    HL POPqq, chkPS,
+    HL POPqq,
     17 BCALL, ( 17 == pushRS )
-;CODE
+;CODE NOP, NOP, NOP,
 CODE 2>R ( 0xb9 )
-    DE POPqq, HL POPqq, chkPS,
+    DE POPqq, HL POPqq,
     17 BCALL, ( 17 == pushRS ) EXDEHL, 17 BCALL,
-;CODE
+;CODE NOP, NOP, NOP,
 CODE R> ( 0xce )
     20 BCALL, ( 20 == popRS )
     HL PUSHqq,

blk/299

@@ -1,10 +1,13 @@
 PC ORG @ 0x1e + ! ( chkPS )
-    HL PUSHqq,
+( Note that you only need to call this in words that push
+  back to PSP. If they don't, calling chkPS is redundant with
+  check in next )
+    EXX,
 ( We have the return address for this very call on the stack
-  and protected registers. 4 - is to compensate that. )
+  and protected registers. 2 - is to compensate that. )
-    HL PS_ADDR 4 - LDddnn,
+    HL PS_ADDR 2 - LDddnn,
     SP SUBHLss,
-    HL POPqq,
+    EXX,
     CNC RETcc,      ( PS_ADDR >= SP? good )
     JR, L2 BWR      ( abortUnderflow-B298 )
 

blk/310

@@ -1,6 +1,5 @@
 CODE PICK
     HL POPqq,
-    chkPS,
     ( x2 )
     L SLAr, H RLr,
     SP ADDHLss,

blk/312

@@ -2,7 +2,6 @@
 CODE 2DROP
     HL POPqq,
     HL POPqq,
-    chkPS,
 ;CODE
 
 ( a b -- a b a b )

blk/322

@@ -1,7 +1,6 @@
 CODE !
     HL POPqq,
     DE POPqq,
-    chkPS,
     (HL) E LDrr,
     HL INCss,
     (HL) D LDrr,

blk/323

@@ -1,7 +1,6 @@
 CODE C!
     HL POPqq,
     DE POPqq,
-    chkPS,
     (HL) E LDrr,
 ;CODE
 

blk/324

@@ -1,7 +1,6 @@
 CODE PC!
     BC POPqq,
     HL POPqq,
-    chkPS,
     L OUT(C)r,
 ;CODE