4f01a66305d21317199b731cc590f52dd286db56 Fix substring operator in macro-processor.

================================ DYNARE MAKE CHECK MATLAB RESULTS ================================ | TOTAL: 432 | PASS: 426 | FAIL: 4 | XFAIL: 2 | XPASS: 0 | LIST OF FAILED TESTS: | * block_bytecode/run_ls2003.m(0,0,0,0) | * block_bytecode/run_ls2003.m(0,1,0,0) | * block_bytecode/run_ls2003.m(1,0,0,0) | * block_bytecode/run_ls2003.m(1,1,0,0)

================================ DYNARE MAKE CHECK OCTAVE RESULTS ================================ | TOTAL: 426 | PASS: 424 | FAIL: 0 | XFAIL: 2 | XPASS: 0

A full log can be found on karaba in '/tmp/dynare-4.4-check-m4ceCCgoaq.log'.