Backporting regeneration of SID when session is missing

from #18
Merge pull request #19 from modcloth/backport-regenerate-sid-for-missing-session

Backporting regeneration of SID when session is missing
Backporting renaming `load_session` method to not conflict with AbstractStore
Merge pull request #21 from modcloth/backport-rename-private-session-loading-method

Backporting renaming `load_session` method to not conflict with AbstractStore
Merge remote-tracking branch 'upstream/v0.2.x-stable'

Conflicts:
	lib/redis-session-store.rb
	redis-session-store.gemspec