Ruby

• ext/bigdecimal/bigdecimal.c (BigDecimal_new): support instantiation a
  BigDecimal object from an Integer.
• test/bigdecimal/test_bigdecimal.rb (test_new_with_integer):
  add for testing the above change.
• ext/bigdecimal/bigdecimal.c (BigDecimal_global_new): replace its body
  with a BigDecimal_new call.
• test/bigdecimal/test_bigdecimal.rb (test_global_new_with_integer):
  add for testing the above change.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@31863 b2dd03c8-39d4-4d8f-98ff-823fe69b080e