Fix the value of PG_UNKNOWN from Alexander Korotkov

Do not use negative values for the PgEdition enumeration, since the bitwise
shifting is used for them in CONTROLFILE_SET_OLDEDITION (see pg_control.h).

+ fix the description of pgpro_utils.c

Author: Marina Polyakova

src/fe_utils/pgpro_utils.c

@@ -4,7 +4,7 @@
  *
  * Copyright (c) 2017, Postgres Professional
  *
- * src/include/fe_utils/pgpro_utils.h
+ * src/fe_utils/pgpro_utils.c
  *
  *-------------------------------------------------------------------------
  */

src/include/common/edition.h

@@ -1,9 +1,13 @@
 #ifndef EDITION_H
 #define EDITION_H
 
+/*
+ * Do not use negative values here, because the bitwise shifting is used for
+ * them in CONTROLFILE_SET_OLDEDITION (see pg_control.h).
+ */
 typedef enum
 {
-	PG_UNKNOWN					= -1,
+	PG_UNKNOWN					= 0xFFFF,
 	PG_ORIGINAL					= 0,
 	PGPRO_STANDARD				= ('P'<<8|'P'),
 	PGPRO_STANDARD_CERTIFIED	= ('P'<<8|'C'),