Fixed bug #317545.

git-svn-id: svn://svn.forge.objectweb.org/svnroot/asm/trunk@1773 271bd773-ee82-43a6-9b2b-1890ed8ce7f9
cherry-pick of lrytz/scala 7f5a93999a
Make MethodWriter public.

And add some accessors. This is all scala-driven.
CustomAttr class.
sbt build.