fix bug with fractional seconds on some locales (SF#1815517: https://sourceforge.net/tracker2/?func=detail&aid=1815517&group_id=13478&atid=113478)

test/test_flac.sh

@@ -17,6 +17,9 @@
 #  restrictive of those mentioned above.  See the file COPYING.Xiph in this
 #  distribution.
 
+# we use '.' as decimal separator in --skip/--until tests
+export LANG=C LC_ALL=C
+
 die ()
 {
 	echo $* 1>&2