Fix tolerance problem in matlab FaustTest.testcat.

It happened rarely:
Verification failed in FaustTest/testcat.

    ---------------------
    Framework Diagnostic:
    ---------------------
    verifyEqual failed.
    --> The values are not equal using isequaln.
    --> The error was not within absolute tolerance.
    --> Failure table:
            Index     Subscripts        Actual             Expected              Error              RelativeError        AbsoluteTolerance
            ______    __________    _______________    ________________    _________________    _____________________    _________________

            110629    (517,187)     342279799020.63    342279799020.631    -0.00115966796875    -3.38807014631939e-15          0.001

    Actual Value:
        592x507 double
    Expected Value:
        592x507 double

    ------------------
    Stack Information:
    ------------------
    In /Users/ci/builds/Z-XUzYP3/0/faustgrp/faust/misc/test/src/Matlab/FaustTest.m (FaustTest.testcat) at 582

misc/test/src/Matlab/FaustTest.m

@@ -577,9 +577,9 @@ classdef FaustTest < matlab.unittest.TestCase
 						D = [F H_];
 					end
 					this.verifyEqual(full(C), full(D), 'AbsTol', 1e-11)
-					this.verifyEqual(full(C), cat(dimcat, full(F),full(H)),'AbsTol', 1e-3)
+					this.verifyEqual(full(C), cat(dimcat, full(F),full(H)),'RelTol', 1e-14)
 					C = cat(dimcat,F,H);
-					this.verifyEqual(full(C), cat(dimcat, full(F),full(H)),'AbsTol', 1e-3)
+					this.verifyEqual(full(C), cat(dimcat, full(F),full(H)),'RelTol', 1e-14)
 				end
 			end
 			% test random number of Fausts concatenation