CJK cleanups. Correct handling when the cursor is covering the

right-hand half of a CJK wide character; correct handling of cut and
paste when CJK text wraps between lines _irrespective of the parity
of the starting column_; correct handling of wordness values
irrespective of which half of a CJK character the user
double-clicked on; correct handling when any terminal activity
overwrites only one half of a CJK wide character. I think we now
behave marginally better than xterm in this respect (it has a redraw
problem when you overwrite the RH half of a CJK char), so I'm happy.
Also redefined the internal UCSWIDE marker to something in the
surrogate range, while I'm here, so that U+303F is available for use
by actual users.

[originally from svn r2426]

putty.h

@@ -51,6 +51,7 @@ typedef struct terminal_tag Terminal;
 #define LATTR_BOT    0x03000000UL
 #define LATTR_MODE   0x03000000UL
 #define LATTR_WRAPPED 0x10000000UL
+#define LATTR_WRAPPED2 0x20000000UL
 
 #define ATTR_INVALID 0x00FF0000UL
 
@@ -69,7 +70,15 @@ typedef struct terminal_tag Terminal;
 #define DIRECT_FONT(c) ((c&0xFE00)==0xF000)
 
 #define UCSERR	     (ATTR_LINEDRW|'a')	/* UCS Format error character. */
-#define UCSWIDE	     0x303F
+/*
+ * UCSWIDE is a special value used in the terminal data to signify
+ * the character cell containing the right-hand half of a CJK wide
+ * character. We use 0xDFFF because it's part of the surrogate
+ * range and hence won't be used for anything else (it's impossible
+ * to input it via UTF-8 because our UTF-8 decoder correctly
+ * rejects surrogates).
+ */
+#define UCSWIDE	     0xDFFF
 
 #define ATTR_NARROW  0x20000000UL
 #define ATTR_WIDE    0x10000000UL