[1.9] The "." dir should not be in load path, but we also put it in CLASSPATH

Ruby 1.9 no longer includes the "." dir in the default load path. We can make this change, and JRUBY-5251 tracks the progress of that fix (and a related bug). However, we also include "." in the default CLASSPATH, which means even if it's not in load path, we will eventually still find resources in the current directory.

There are a couple possible routes here:

• Ignore it, and just accept that CLASSPATH and load path are different. I'm not sure this is an option, since it will cause us to always deviate on whether we find resources in the current directory.
• At startup, don't include . in CLASSPATH. Currently, in both jruby.bash and the native launcher, I think we include "." explicitly. We could turn that off, if so.

Of course, system-global CLASSPATH settings would be impossible to modify.