fix of 2 bugs when checking VCS requirements

1. snvAvailable variable was misspelled therefor not found
2. proc_close() sometimes retunres 1 which is OK but  the implementation
was converting it to false on VCS requirement check. I changed it to
check if the result is different than -1 which is the only case of error
according to the documentation:
http://php.net/manual/en/function.proc-close.php