Add Producer.retry

This implementation allows API consumers the choice of retry strategy
without being overly burdensome.
updated for Xcode 6 beta 5
Bag.swift: Indentation + whitespace
Atomic.swift: indentation
Action.swift: indentation
Updated swiftz ref
remove internal func specifiers, fix Disposable.disposed
update swiftz ref
fix other Atomic bool cases
Compare Disposable data to nil, not false
Merge pull request #1454
Circumvent "cannot reference local function" errors
Get rid of "__conversion()", no longer supported
Temporarily switch to pyrtsa/swiftz to fix the "local function" error
Switch back to master on maxpow4h/swiftz
Merge pull request #1475 from pyrtsa/fix/beta6-issues

Fix issues with Beta 6
Signal.current was never meant to be recursive

Access the backing property instead.
Actually fix access of _current property
Merge branch 'swift-development' into retry
Update for new Optional behavior