Context management changes:

Watch and warn for requests created on dead contexts.
Always load bitmaps with the application context:
  Loads can not actually be cancelled when started (only if deferred).
  Since bitmap loads are coalesced, make sure that they are not cancelled
  if loaded in one context, which died, but is still in use in another.
Merge branch 'master' of https://github.com/koush/ion

# By Koushik Dutta
# Via Koushik Dutta
* 'master' of https://github.com/koush/ion:
  Context management changes: