Fixed exception throwing from async methods. Test added.
(grafted from dcb483023b0ac34c59d8e672fbf7fccde38e334e)

--HG--
extra : source : dcb483023b0ac34c59d8e672fbf7fccde38e334e
Merge pull request #573 from iskiselev/AsyncExceptions

Fixed exception throwing from async methods. Test added.