The libssh2 library is needed to connect to the homedir/quota server via SSH.
You can get libssh2 here: http://www.libssh2.org Unpack the package and install it by executing the commands "./configure", "make" and "make install" in the extracted directory. Several Linux distributions already include a package for libssh2.
Several Linux distributions already include a package (e.g. libssh2-php).
Otherwise, run "pecl install ssh2-beta". If you have no pecl command then install the PHP Pear package (e.g. php-pear or php5-pear) for your distribution.
If you want to compile it yourself, get the sources here: http://pecl.php.net/package/ssh2
After installing the PHP module please add this line to your php.ini:
extension=ssh2.so