Rewrite -concat to avoid a recursive block
Add debug logging methods to RACSignal
Merge pull request #237 from github/concat-block-cycle

Rewrite -concat to avoid a recursive block
Merge pull request #240 from github/signal-logging

Add debug logging methods to RACSignal
Merge remote-tracking branch 'origin/master' into multicast
weakify/strongify
use an init instead of a class method
consistent naming
doc updates
more tests