Add Producer.retry

This implementation allows API consumers the choice of retry strategy
without being overly burdensome.
Add errorHandler parameter to Producer.bindTo

This emphasizes the fact that errors must get handled somehow in a
binding, or else that the caller is guaranteeing they won’t occur.
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