Adding the ability to read Streams from svn.
Adding the ability to read Streams from svn.

Previously, Streams were only used for outputs in diff calls, but
Revision#get_contents will return a Stream that returns the file contents. This
commit adds a Stream#read function and a Stream#to_string_io function to make
the contents of these Streams accessible.

codefoundry/svn,rdblue/svn