Updating some golang defaults

to set 1.3 as the default version and to use the new gvm binary download if possible.
That was my bad.  `gvm install go1.3` works fine, but for `--prefer-binary`, it must be just the raw version (ie, `gvm install 1.3 --prefer-binary`) since it's used directly to construct the path (so we get "gogo1.3..." in the first case).