Add and improve Ruby test cases in the context of nesting and namespaces

This is done in preparation for adding namespace support to the Ruby
part of SWIG. Some existing test cases were reorganized or duplicated
for flat/nonflat nesting. For some a Ruby test script was added.
Finally the ruby/Makefile.in was improved so that for test cases
without an explicit test script, the generated wrapper library will
be loaded by the Ruby interpreter to ensure loading works fine.

Examples/test-suite/ruby/nested_scope_flat_runme.rb

@@ -0,0 +1,25 @@
+#!/usr/bin/env ruby
+#
+# Check the availability of expected classes and their member variables.
+#
+
+require 'swig_assert'
+require 'nested_scope_flat'
+
+Nested_scope_flat::Global_.new
+Nested_scope_flat::Outer1.new
+nested2 = Nested_scope_flat::Nested2.new
+nested2.data = 42
+swig_assert_equal("nested2.data", "42", binding)
+Nested_scope_flat::Klass.new
+
+Nested_scope_flat::Abstract_int
+cannot_instantiate = false
+begin
+  Nested_scope_flat::Abstract_int.new
+rescue TypeError
+  cannot_instantiate = true
+end
+swig_assert_simple(cannot_instantiate)
+
+Nested_scope_flat::Real.new.Method()