Script for running tests on multiple cores.

There is a new script called par_vvp_reg.pl. It depends on Parallel::ForkManager (available in CPAN) to run iverilog & vvp instances in separate processes to decrease the time required to perform tests on modern CPUs.
I have managed to go down from ~1 minute to ~15 seconds on 8-core i7 with SSD. The approximate performance boost increases linearly up to 4 cores, then the difference becomes insignificant.
You may specify the number of used processes by appending a number, e.g. "./par_vvp_reg.pl 8" runs with 8 processes. Otherwise the number of available cores is autodetected (works only in Linux, relies on /proc/cpuinfo).
If you like the results, I may modify other test scripts as well.

*Remarks:*
* I modified fscanf* tests, because they were using the same file and therefore stayed in conflict. It does not change anything for the default vvp_reg.pl script.
* The output is not fully compatible with the default output stored in the repository. I decided to sort the test results in lexical order, otherwise the order would be random each run (depends on the time when a test ends).
* There are two tests (pr2509349a & sys_func_task_error) that I could not fix. I guess this might be a result of changing the iverilog output file name from vsim to $tname.vsim (to avoid conflicts). I did not modified them, because I do not want to break the default test scripts.
* Output files are saved in the main directory, they are removed at the end of the script. I do not remove ivl_vhdl_work directory between tests, because it could be used in another process. More elegant solution would be to use separate directories. If you think this is completely wrong - please let me know.
* This is the first time I write code in Perl, therefore I am not sure if everything is done in accordance with the art.