Explicitly declare a few properties as atomic.

These are already implicitly atomic, so this doesn't change the
semantics.  It does silence some warnings though (from
CLANG_WARN_OBJC_IMPLICIT_ATOMIC_PROPERTIES).
Fix possible crash in  [NSCalendar components:fromDate:], probably when logMessage->timestamp is not set
Update calendarUnitFlags with new iOS SDK values (should work on older systems as long as they are compiled agains iOS 6+ SDK)
Merge pull request #277 from rivera-ernesto/fix_calendar_crash

Fix calendar crash
Merge pull request #258 from tipbit/atomic-property-warnings

Explicitly declare a few properties as atomic.