IO.pod: add barebones spec for 'open' based on the syntax the tests have. 
IO.pod: add barebones spec for 'open' based on the syntax the tests have. 

git-svn-id: 53605643c415f7495558be95614cf14171f1db78@13284 c213334d-75ef-0310-aa23-eaa082d1ae64

prammer/specs,tokuhirom/specs,perl6/specs,perl6/specs,prammer/specs,tokuhirom/specs,tokuhirom/specs,prammer/specs