--- configure.ac	2007-01-31 00:09:02.000000000 +0100
+++ configure.ac_new	2007-01-31 00:45:53.000000000 +0100
@@ -66,10 +66,16 @@
 AC_PROG_MAKE_SET
 AC_PROG_YACC
 
+AC_ARG_WITH(fftw,
+	    [  --with-fftw             use fftw3],
+	    [with_fftw=$withval],
+	    [with_fftw="no"])
+if test "$with_fftw" = "yes"; then
 AC_CHECK_HEADER(fftw3.h,
    AC_CHECK_LIB([fftw3], fftw_execute,,
            AC_MSG_NOTICE([*** Could not find libfftw3: will compile without optional fast Fourier transforms. ***])),
      AC_MSG_NOTICE([*** Header file fftw3.h not found: will compile without optional fast Fourier transforms. ***]))
+fi
 
 GCVERSION=6.8
 
@@ -152,11 +158,17 @@
 		   [Define if you have a working <rpc/rpc.h> header file])],
    AC_MSG_WARN([*** Broken rpc headers; XDR support disabled ***]))
 
+AC_ARG_WITH(gsl,
+	    [  --with-gsl              use gsl libraries],
+	    [with_gsl=$withval],
+	    [with_gsl="no"])
+if test "$with_gsl" = "yes"; then
 AC_CHECK_HEADER(gsl/gsl_sf.h,
    AC_CHECK_LIB([gsl], gsl_sf_Si, [AC_DEFINE(HAVE_LIBGSL, 1,
    [Define to 1 if you have the 'gsl' library (-lgsl). ]) LIBS=$LIBS"-lgsl -lgslcblas "],
            AC_MSG_NOTICE([*** Could not find libgsl: will compile without optional special functions. ***]),[-lgslcblas]),
      AC_MSG_NOTICE([*** Header file gsl_sf.h not found: will compile without optional special functions. ***]))
+fi
 
 # Checks for typedefs, structures, and compiler characteristics.
 AC_TYPE_PID_T