SI-7198 Par-Test uses filters files

Partest will also read files/filters and files/kind/filters for
filter expressions (one per line, trimmed, leading #comments)
which are taken as regexes.

A test/files/filters is provided which attempts to quell HotSpot
warnings; the test for this commit requires it.

The elided lines can be revealed using the lemon juice of verbosity:

apm@mara:~/projects/snytt/test$ ./partest --verbose --show-diff files/run/t7198.scala
[snip]
>>>>> Transcripts from failed tests >>>>>

> partest files/run/t7198.scala
% scalac t7198.scala
[snip]
% filtering t7198-run.log
--Over the moon
--Java HotSpot(TM) 64-Bit Server VM warning: Failed to reserve shared memory (errno = 28).

The filtering operation is part of the transcript, which is printed on failure.

No attempt is made to be clever about not slurping the filters file a thousand times.

Previous literal patterns had to be updated because there's parens in them thar strings.

Future feature: pattern aliases, define once globally and invoke in test filters.