Make STRICTENC invalid pubkeys fail the script rather than the opcode.

This turns STRICTENC turn into a softforking-safe change (even though it
is not intended as a consensus rule), and as a result guarantee that using
it for mempool validation only results in consensus-valid transactions in
the mempool.

src/script/script_error.h

@@ -42,6 +42,7 @@ typedef enum ScriptError_t
     SCRIPT_ERR_SIG_PUSHONLY,
     SCRIPT_ERR_SIG_HIGH_S,
     SCRIPT_ERR_SIG_NULLDUMMY,
+    SCRIPT_ERR_PUBKEYTYPE,
 
     /* softfork safeness */
     SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS,