analog: Add MQ Flag for four-wire measurements

On the high-end bench multimeters, resistance can be measured with a
kelvin connection as well as the more common two wire method. Provide
a flag which can indicate if four-wire mode is used.

include/libsigrok/libsigrok.h

@@ -383,6 +383,8 @@ enum sr_mqflag {
 	SR_MQFLAG_REFERENCE = 0x80000,
 	/** Unstable value (hasn't settled yet). */
 	SR_MQFLAG_UNSTABLE = 0x100000,
+	/** Measurement is four wire (e.g. Kelvin connection). */
+	SR_MQFLAG_FOUR_WIRE = 0x200000,
 
 	/*
 	 * Update mq_strings[] (analog.c) and fancyprint() (output/analog.c)

src/analog.c

@@ -114,6 +114,7 @@ static struct unit_mq_string mq_strings[] = {
 	{ SR_MQFLAG_AVG, " AVG" },
 	{ SR_MQFLAG_REFERENCE, " REF" },
 	{ SR_MQFLAG_UNSTABLE, " UNSTABLE" },
+	{ SR_MQFLAG_FOUR_WIRE, " 4-WIRE" },
 	ALL_ZERO
 };
 

src/output/analog.c

@@ -273,6 +273,8 @@ static void fancyprint(int unit, int mqflags, float value, GString *out)
 		g_string_append_printf(out, " REF");
 	if (mqflags & SR_MQFLAG_UNSTABLE)
 		g_string_append_printf(out, " UNSTABLE");
+	if (mqflags & SR_MQFLAG_FOUR_WIRE)
+		g_string_append_printf(out, " 4-WIRE");
 	g_string_append_c(out, '\n');
 }