Make StraceRunner handle programs that spawn multiple sub-processes

This is an issue Tim Docker brought up in the mailing list. Here's his 
message:

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I have had some troubles with an older version of fabricate (1.08)
relating to the way the StraceRunner was handling the current working
directory when subprocesses were involved. I see that an attempt has
been made to fix this in more recent versions, by keeping a stack of
working directories.

But is this stack based approach correct? Given that it's possible for
different subprocesses to be executing simultaneously (and hence have
interleaved file access output in strace), I would have though that a
dictionary of working directories should be kept, indexed by pid, with

 - new entries created by fork/clone matches
 - entries updated by chdir matches
 - entries removed by exit matches
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Original issue reported on code.google.com by benh...@gmail.com on 7 Dec 2009 at 11:25

Zomega / fabricate

Make StraceRunner handle programs that spawn multiple sub-processes #24