Merge pull request #90 from kgoodier/develop-next

Fix redirects and unretained metadata property.
Canonicalize requests.

Fixes:
- empty path becomes "/"
- add default user-agent

Code taken from an Apple sample and slightly modified for our purposes.
This duplicates some of what NSURLRequest+SPDYURLRequest.m provides in
allSPDYHeaderFields, but since that method has to rebuild the path +
query + fragment anyway, it's unavoidable.
Add "unregisterAllAliases" to SPDYProtocol.
SPDY assertion handler fix.

Apply a custom assertion handler to the NSURL thread that CocoaSPDY
operates on; it will print out the failure and callstack, then raise
an NSInternalInconsistencyException exception on the main thread.

This is necessary because an NSAssert, at least in iOS, on the NSURL
thread seems to stop its execution but not kill the process or otherwise
alert the app, as expected by an assertion failure.