Updated the bittorrent-sync.install file to fix a few bugs and issues.
PKGBUILD file was also updated with new sha256sum.

Changed the post_install() if statement to be correct.
Before it was missing quotes around the grep command, so it was causing an error when evaluated.
Also the comparison operator was set to "!=" when it should have been "==" so as to create a new user when no old one was found.