make using the context classloader configurable

When run inside a JBoss AS 7 module the native libraries fail to load due to
using the root classloader. The context classloader can/should be used. This
commit adds a system property, org.xerial.snappy.use.context.classloader, that
if set to true will cause SnappyLoader to use the context classloader to load
the native snappy library.

I am also changing the artifact version to 1.0.5-M3-p1 to indicate that this is
a patched version.