Fix conflicting types.

--- ext/gsl_native/matrix_complex.c.orig	Fri Jul  3 11:19:42 2015
+++ ext/gsl_native/matrix_complex.c	Sun Jul 19 19:03:38 2015
@@ -1521,7 +1521,7 @@ static VALUE rb_gsl_matrix_complex_indgen_singleton(in
 // Starting with version 1.15, GSL provides a gsl_matrix_complex_equal
 // function, but it only determines absolute equality (i.e. is has no epsilon
 // argument).
-static int gsl_matrix_complex_equal_eps(const gsl_matrix_complex *m1,
+static int gsl_matrix_complex_equal_with_eps(const gsl_matrix_complex *m1,
                                         const gsl_matrix_complex *m2, double eps)
 {
   gsl_complex z1, z2;
@@ -1556,7 +1556,7 @@ static VALUE rb_gsl_matrix_complex_equal(int argc, VAL
   Data_Get_Struct(obj, gsl_matrix_complex, m1);
   CHECK_MATRIX_COMPLEX(argv[0]);
   Data_Get_Struct(argv[0], gsl_matrix_complex, m2);
-  ret = gsl_matrix_complex_equal_eps(m1, m2, eps);
+  ret = gsl_matrix_complex_equal_with_eps(m1, m2, eps);
   if (ret == 1) return Qtrue;
   else return Qfalse;
 }
