Fix sscanf() truncating input from thousands separator

Per Github issue Hamlib#1704, N3FJP logger sends a string with an embedded
comma for frequencies above 1 GHz resulting in such frequencies being
truncated.  This patch uses the optional apostrophe character in the
sscanf() format string to ignore the thousands separator.

A possible bug is when the locale of the system on which libhamlib is
executing uses a dot for the thousands separator rather than a comma.
It is unclear if the N3FJP software obeys such locales or not.  If this
turns out to be an issue then this fix will need to be reconsidered.

Author: N0NB

rigs/dummy/aclog.c

@@ -461,7 +461,7 @@ static int aclog_get_freq(RIG *rig, vfo_t vfo, freq_t *freq)
     char *p = strstr(value, "<FREQ>");
     *freq = 0;
 
-    if (p) { sscanf(p, "<FREQ>%lf", freq); }
+    if (p) { sscanf(p, "<FREQ>%'lf", freq); }
 
     *freq *= 1e6; // convert from MHz to Hz