Add support for cancellation to our pycurl downloader.
Refactored remove command to be polling-based
Correct my spelling of canceled vs. cancelled to be consistent.
Merge pull request #407 from pulp/jdob-remove-command

Refactored remove command to be polling-based
Merge pull request #404 from pulp/rbarlow_pycurl_cancellation

Add support for cancellation to our pycurl downloader.
Merge branch 'master' into jconnor-other-downloader-implementations

Conflicts:
	platform/test/unit/server/test_common_download_backends_curl.py
fixed is_canceled