Fix the guards around the got_chunk emission so that it doesn't get messed

Fix the guards around the got_chunk emission so that it doesn't get messed

	* libsoup/soup-message-io.c (read_body_chunk): Fix the guards
	around the got_chunk emission so that it doesn't get messed up if
	you pause the I/O from the got_chunk handler. (#452280, Marco
	Barisione).
	(soup_message_io_pause, soup_message_io_unpause): Update docs
	again; these are now allowed with client-side I/O as well. Fix
	unpause() to unpause asynchronously on async sockets.

	* libsoup/soup-session-async.c (send_message): Iterate session's
	async_context, not the default main context.

	* tests/pull-api.c: Test/sample of creating a pull-style API using
	SoupSessionAsync.

	* tests/index.txt: new file to act as DirectoryIndex for the
	tests. (In particular, pull-api wants this to be largeish.)

svn path=/trunk/; revision=952