Add SUDO_CONV_PROMPT_MASK define which corresponds to the "pwfeedback"

sudoers option.  Do not disable echo if TGP_ECHO is set.

src/sudo.h

@@ -88,7 +88,7 @@
 #define TGP_ECHO	0x01		/* leave echo on when reading passwd */
 #define TGP_STDIN	0x02		/* read from stdin, not /dev/tty */
 #define TGP_ASKPASS	0x04		/* read from askpass helper program */
-#define TGP_FEEDBACK	0x08		/* visual feedback during input */
+#define TGP_MASK	0x08		/* mask user input when reading */
 
 struct user_details {
     uid_t uid;