* add 'flag:unread' as a synonym for 'flag:new OR NOT flag:seen'

- update documentation
  - update test cases
  - some cleanups in the C++-code
  - bump the database version, to trigger the --rebuild warning

src/mu-msg-flags.h

@@ -56,14 +56,19 @@ enum _MuMsgFlags {
 	/* "F"->flagged message */
 	MU_MSG_FLAG_FLAGGED	= 1 << 6,
 
+	/* "U"->unread message; it's a pseudo/convenience flag that
+	 * means (NEW or not SEEN) */
+	MU_MSG_FLAG_UNREAD      = 1 << 7,
+	
+	
 	/* these we get from the contents */
 	
 	/* "Z"->signed message */
-	MU_MSG_FLAG_SIGNED      = 1 << 7,
+	MU_MSG_FLAG_SIGNED      = 1 << 8,
 	/* "X"->encrypted message */
-	MU_MSG_FLAG_ENCRYPTED   = 1 << 8,
+	MU_MSG_FLAG_ENCRYPTED   = 1 << 9,
 	/* "A"->message has attachment */
-	MU_MSG_FLAG_HAS_ATTACH  = 1 << 9
+	MU_MSG_FLAG_HAS_ATTACH  = 1 << 10
 };
 typedef enum _MuMsgFlags MuMsgFlags;