Replace hard-coded exit status bitmask values with named constants.

src/include/pv.h

@@ -23,6 +23,17 @@
 extern "C" {
 #endif
 
+/*
+ * Exit status bitmask values.
+ */
+#define PV_ERROREXIT_REMOTE     1
+#define PV_ERROREXIT_ACCESS     2
+#define PV_ERROREXIT_OUROBOROS  4
+#define PV_ERROREXIT_TRANSITION 8
+#define PV_ERROREXIT_TRANSFER   16
+#define PV_ERROREXIT_SIGNAL     32
+#define PV_ERROREXIT_MEMORY     64
+
 /*
  * Opaque structure for PV internal state.
  */