for issue 360 - a  better way to qeury the verison of reltool

This is an attempted "fix" on issue360. Basically, it is just detection of otp release version as commented in the TODO in check_vsn. 

If detects of prior to R14A it uses the original code, if not, use the code submit in 
https://github.com/basho/rebar/commit/6996cd4fcc9dbd80591db38fd3cccfc8ee4aec16