Fix missing "arch" command at testing

test with --arch option runs ruby via `arch' command.
`arch' command was missed in test_loadlibs() and test_testcase().

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2427 f4f36d40-9719-0410-9868-dde021a23eda