lal: mark as version 7.3.1

lal/configure.ac

 AC_PREREQ([2.63])
-AC_INIT([LAL],[7.3.0.1],[lal-discuss@ligo.org])
+AC_INIT([LAL],[7.3.1],[lal-discuss@ligo.org])
 AC_CONFIG_HEADERS([lib/config.h lib/LALConfig.h])
 AC_CONFIG_SRCDIR([lib/std/LALStdio.h])
 AC_CONFIG_AUX_DIR([gnuscripts])