Follow-up to r1442063: Fix broken ruby bindings build on Windows.

r1442063 turned the Windows compiler warning C4204 "nonstandard extension
used : non-constant aggregate initializer" into an error.  The Ruby bindings
uses a few such offending initializers and thus needs some minor tweaks to
be build again. 

* subversion/bindings/swig/ruby/libsvn_swig_ruby/swigutil_rb.c
  (rb_set_pool_if_swig_type_object,
   r2c_hash,
   invoke_callback): Declare and initialize arrays/structs in separate
   statements.



git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1480442 13f79535-47bb-0310-9956-ffa450edef68