[parser] adding chunked shuffle as a C function (writes each line to one of n random files, runs shuf on each file and concatenates the result). Adding a version which allows specifying a specific chunk size, and using a 2GB limit for address parser training. Allowing gshuf again for Mac as it seems the only problem there was not having enough memory when testing on a Mac laptop. The new limited-memory version should be fast enough.

configure.ac

@@ -57,8 +57,10 @@ AC_CONFIG_FILES([Makefile
                  test/Makefile])
 
 AC_CHECK_PROG([FOUND_SHUF], [shuf], [yes])
+AC_CHECK_PROG([FOUND_GSHUF], [gshuf], [yes])
 
 AS_IF([test "x$FOUND_SHUF" = xyes],  [AC_DEFINE([HAVE_SHUF], [1], [shuf available])])
+AS_IF([test "x$FOUND_GSHUF" = xyes],  [AC_DEFINE([HAVE_GSHUF], [1], [gshuf available])])
 
 # ------------------------------------------------------------------
 # Checks for SSE2 build