only initialize the schema for the first thread accessing a realm at a particular path
fix for swift tests
cleanup table creation flow, use only 1 transaction during migrations
fix for async test conditions
fix for reusing cached objectSchema tables
use const for non-versioned version number
api cleanup
changelog
changelog
add test for notifications in bg threads
Merge pull request #807 from realm/al-no-double

Fix for unexpected notifications when creating background RLMRealms