If server binary download fails, the broken file will be cached #2

During download of the binary on the server (in linux via install.sh, untested on other platforms), the download is made directly to the destination file which may result in an incomplete download being left behind.

Recommendations:

1. Download to a temp file in the same dir (such as .filename.temp1234 and then move the file to the destination once the download succeeds.
2. Check the checksum of the downloaded file with the server. We have SHA1 checksums serverside (idk if we expose them as a file in the bin dir but we could start doing that).