Issue #370: Fix problem where stream errors would not be detected

It seems the comparison has always been against the wrong enum, so the check would never trigger previously.

The latest llvm issues a warning like this:
ASIDataDecompressor.m:161:34: Comparison of constant 'NSStreamEventErrorOccurred' (8) with expression of type 'NSStreamStatus' (aka 'enum NSStreamStatus') is always false

[patch from github user 'OpenFibers', thanks!]
Fix an analyser warning in the latest llvm

Error is: ASIHTTPRequest.m:4571:44: Division by zero

I think this may be a false warning, or llvm is assuming that "[bandwidthUsageTracker addObject:...];" has failed for some reason, but it does no harm to double check that we're not going to divide by zero.
Updated deprecated method 

addTimeInterval changed to dateByAddingTimeInterval
Merge pull request #375 from mineschan/master

Updated deprecated method addTimeInterval
Restored compatibility with OS X 10.5
Suppress deprecation warning in Xcode 5
Merge pull request #380 from AriX/master

Restored compatibility with OS X 10.5
fixed ios7 warnings for dismissModalViewControllerAnimated vs dismissViewControllerAnimated:completion: etc
backwards compatibility for < iOS 5
Merge pull request #384 from graceful/ios7-warnings

Fix iOS 7 warnings for dismissModalViewControllerAnimated and presentModalViewController
Avoid warnings about implicit integer conversions that change the
signedness of an integer value (-Wsign-conversion).
Avoid warnings about @property declarations that are implicitly atomic
(-Wno-implicit-atomic-properties).