Only cache the latest items in the time window
OperatorBuffer
OperatorConcat
Rename concat test
OperatorCombineLatest
OperatorDefaultIfEmpty
OperatorDefer
OperatorDematerialize
OperatorDistinct
OperatorDistinctUntilChanged
OperatorFinallyDo
OperatorMergeMap
OperatorToObservableFuture
Merge pull request #1065 from zsxwing/skip-last-timed

Optimize OperatorSkipLastTimed
Merge pull request #1073 from akarnokd/OperatorBuffer

OperatorBuffer
Merge pull request #1074 from akarnokd/OperatorConcat

OperatorConcat
Merge branch 'OperatorCombineLatest' of github.com:akarnokd/RxJava into merge-prs

Conflicts:
	rxjava-core/src/main/java/rx/Observable.java
Merge branch 'OperatorDefaultIfEmpty' of github.com:akarnokd/RxJava into merge-prs

Conflicts:
	rxjava-core/src/main/java/rx/Observable.java
Merge branch 'OperatorDefer' of github.com:akarnokd/RxJava into merge-prs

Conflicts:
	rxjava-core/src/main/java/rx/Observable.java
Merge branch 'OperatorDematerialize' of github.com:akarnokd/RxJava into merge-prs

Conflicts:
	rxjava-core/src/main/java/rx/Observable.java