Milestone 2: Write each frequency results into its own files

[bangerth]

From Jason:

One thing that I had to do with biharmonic was to have it write each frequency result to it's own file. I tried to use frequency_response.txt, but I'd get read/write collision errors when your solver and Ares were both trying to access it at the same time.

[bangerth]

Specifically:

<freq #>_frequency_response.txt

This is an output file generated by dealII_3D. A separate file will be created for every frequency listed in <cmd_filename>. <freq #> will be a numeric number from 1 to N, where N is the number of frequencies to solve. For instance, for the <cmd_filename> example given above, five files will be created:

T1_1_frequency_response.txt
T1_2_frequency_response.txt
T1_3_frequency_response.txt
T1_4_frequency_response.txt
T1_5_frequency_response.txt

[bangerth]

Fixed by 146dee7.