add 'exclude' ability to BlockDownloadVerify-injector.pl

Original Savannah ticket 88062 reported by ratnik on Mon Oct 24 03:09:22 2011.

Natalia has requested the ability to exclude blocks/datasets from being injected for the BDV agent

I think we should mimic the way GnU tar handles exclusion, adding two extra options:

--exclude REGEX
--exclude-from FILE

--exclude can be repeated, and specifies patterns which are matched against the full block name. Matching blocks are excluded from the test. --exclude-from need not be repeated, and specifies a file which contains a list of patterns, all of which are applied, like multiple --exclude options.

N.B. There's no reason not to allow both --exclude and --exclude-from in the same invocation.