Small Leak in Fileno Bookkeeping For STDIO RubyIOs

Every time RubyIO's constructor that accepts a STDIO as the 2nd argument it called it calls runtime.putFilenoMap to keep track of internal to external filenos for these special streams. This ultimately ends up putting key/value integer pairs in Ruby's filenoExtIntMap and filenoIntExtMap, the latter which grows in size every time this RubyIO constructor is called. When the RubyIO gets closed its entry in filenoIntExtMap does not get cleaned up and thus that map has the potential to grow indefinitely.

The bug is marked as minor because this is only an issue if large numbers of STDIO RubyIOs are created in a single runtime. The proposed fix is to delete the entries out of filenoIntExtMap in OpenFile's finalize method or somewhere else appropriate that gets called on both close and finalization of RubyIOs.