Use the Java 6 like services approach to find all supported
TransportProtocols within the CLASSPATH and load them all for use.
This allows users to inject additional protocol implementations simply
by putting their JARs on the application CLASSPATH, provided the
protocol author has written the proper services file.
Change-Id: I7a82d8846e4c4ed012c769f03d4bb2461f1bd148 Signed-off-by: Shawn O. Pearce <spearce@spearce.org>