Media.setVolume caused the application to crash after Media.release was
called. Code causing crash:

  var m = new Media("test.caf");
  m.release();
  m.setVolume(1); // crash in this call

The reason was that retrieving the CDVAudioFile instance from the sound
cache would return nil after Media.release. This patch fixes the issue
by explicitely checking for nil. It also does away with an unnecessary
cache initialization, which isn't needed as -[Media setVolume:] doesn't
write to the cache.

Signed-off-by: Michael Hanselmann <public@hansmi.ch>

Change to use amazon-fireos as a platform if the user agent string contains 'cordova-amazon-fireos'

Conflicts:
	src/windows8/MediaProxy.js

[CB-4847] iOS 7 microphone access requires user permission - if denied, CDVCapture, CDVSound does not handle it properly

Revert "[CB-4847] iOS 7 microphone access requires user permission - if denied, CDVCapture, CDVSound does not handle it properly"

This reverts commit 0259d766.

[CB-4847] iOS 7 microphone access requires user permission - if denied, CDVCapture, CDVSound does not handle it properly