fix threading login in page getting

squashed:

debug log for HTTPError

removed extraneous call to logger

block on queue.get and reuse worker threads

remove unused thread lock obj

just use a fixed 10 worker threads

update docstring

Move the thread queue management and variables from method to instance

Since the pool of workers gets reused, this seems the cleanest way
to ensure that excess threads aren't created as they no never return

because the queue is only ever used for one req at a time, it seems safe
to reuse it on the PackageFinder instance as _get_pages is called through:

prepare_files - find_requirement - _get_pages

fix thread args - remove unused queue size call

move ALL the thread getting state onto self

no sharing of seen and req variables

stub of thread helper class

better threading support for PackageFinder

adds a helper class that manages a threads and queue for page/link scraping

removed duplicate class stub

another glitch of the cherry-pick merge

merge cleanup