Enhancement of "Retrieve All Embedded Resources": Allow exceptions specificed by regex

[asfimport]

Vic Wong (Bug 40945):
I have been load testing a set of pages that access some off-site tracking
resources that I would like to leave out, since they are generating a great deal
of unnecessary latency that doesn't represent my own server load.

I see that Enhancement request: 40933 hopes to address a similar issue, but I
think a more robust solution rather than filtering by "same server" (which
doesn't account for other internal servers that I would want to load test) would
be using regex to specify exceptions.

That way, one could exclude any arbitrary resource defined by URL, inclusing
file extension, hostname, etc..

OS: other

[asfimport]

Sebb (migrated from Bugzilla):
The code has been added to SVN; will be in nightlies after r516782.