Create `defer` syntax and `OP_PUSHDEFER` opcode

Adds syntax `defer { BLOCK }` to create a deferred block; code that is
deferred until the scope exits. This syntax is guarded by

  use feature 'defer';

Adds a new opcode, `OP_PUSHDEFER`, which is a LOGOP whose `op_other` field
gives the start of an optree to be deferred until scope exit. That op
pointer will be stored on the save stack and invoked as part of scope
unwind.

Included is support for `B::Deparse` to deparse the optree back into
syntax.

1 files changed, 2 insertions, 1 deletions

diff --git a/opnames.h b/opnames.h
index f6c1552a52..a78baab591 100644
--- a/opnames.h
+++ b/opnames.h
@@ -418,10 +418,11 @@ typedef enum opcode {
 	OP_LEAVETRYCATCH = 401,
 	OP_POPTRY	 = 402,
 	OP_CATCH	 = 403,
+	OP_PUSHDEFER	 = 404,
 	OP_max		
 } opcode;
 
-#define MAXO 404
+#define MAXO 405
 #define OP_FREED MAXO
 
 /* the OP_IS_* macros are optimized to a simple range check because