Bugfix: hash_pop: If a work should be rolled, use a clone of it rather than consume a rollable work

This fixes a bug whereby sufficiently active/fast miners could consume rollable work before the work producing thread had a chance to clone it, effectively making it as useless as an unrollable work.
Bugfix: Stratum: Use curl_easy_cleanup to close connection, so cURL understands what is going on
Merge commit 'ae78270' into bfgminer-2.10.x
Merge commit 'd3bf0b0' into bfgminer-2.10.x

Conflicts:
	util.c