Raise v17 training time tolerance, as found in iaxmodem supplied spandsp.

diff -up -r spandsp-0.0.6/src/v17rx.c ../iaxmodem/iaxmodem-1.3.0/lib/spandsp/src/v17rx.c
--- a/src/v17rx.c	2016-02-07 02:24:28.000000000 +0100
+++ b/src/v17rx.c	2014-06-30 18:21:39.000000000 +0200
@@ -1046,10 +1046,10 @@ static void process_half_baud(v17_rx_sta
             s->carrier_track_i = 100.0f;
             s->carrier_track_p = 500000.0f;
 #endif
-            /* TODO: This was increased by a factor of 10 after studying real world failures.
-                     However, it is not clear why this is an improvement, If something gives
-                     a huge training error, surely it shouldn't decode too well? */
-            if (s->training_error < (V17_TRAINING_SHORT_SEG_2_LEN - 8)*4.0f*constellation_spacing[s->space_map])
+            /* We need to be liberally accepting of poor fast-train training errors here.
+               Doing this affords the DTE the opportunity to make some use of whatever 
+               valid Phase C data can be decoded. */
+            if (s->training_error < (V17_TRAINING_SHORT_SEG_2_LEN - 8)*10.0f*constellation_spacing[s->space_map])
             {
                 s->training_count = 0;
                 if (s->bits_per_symbol == 2)