The flow control window will limit the amount of buffered data.

This prevents a caller from getting stale data and/or a stale EOF marker
if a previous caller didn't consume the queue.

Netlib was assuming that PEMReader would return a specific class when
parsing a public key; the latest version returns a different class.

Also patched the descriptor parser to accept fingerprint lines with or
without the opt keyword.

Android UI elements can be destroyed and recreated at any time, and they
can only store serialisable state, so references to long-running tasks
have to take the form of serialisable handles. This is pretty ugly -
it's easy to create memory leaks if you don't clean up stale
handle/reference mappings - but it's less ugly than the common solution
of using static variables to hold references.