test_multirate_squarewave[5-Sq], test_multirate_squarewave[5-Fqs] don't work

Running test_codegen_fortran gets an error on my machine. This is on OS X, gfortran 5.2.

The test passes in the CI server, so perhaps there is some non-deterministic code generation? @inducer, maybe you should look at this.

For multirate_squarewave[5-Sq]:

E                                  RuntimeError: Fortran code has non-empty stderr:
E                                   ERROR: achieved order too low:   4.5003386053096834       <    4.7000000000000002

Fortran output:

 done   7.6923076923076927E-003   1.2152057138337113E-011   6.1106675275368616E-013
 done   5.0000000000000001E-003   1.3935519405094965E-012   8.7929663550312398E-014
 estimated order slow:   5.0272249564398281     
 estimated order fast:   4.5003386053096834 

For multirate_squarewave[5-Fqs]:

E                                  RuntimeError: Fortran code has non-empty stderr:
E                                   ERROR: achieved order too low:   4.6926118304740490       <    4.7000000000000002

Fortran output:

done   7.6923076923076927E-003   9.8383523550182872E-012   6.5880634281256789E-013
done   5.0000000000000001E-003   1.2860823517257813E-012   8.7263529735537304E-014
estimated order slow:   4.7232318566100897     
estimated order fast:   4.6926118304740490