Update phpseclib to latest Git snapshot

Signed-off-by: Michal Čihař <michal@cihar.com>
Allow to use system phpseclib

Signed-off-by: Michal Čihař <michal@cihar.com>
Adjust tests to new IV logic

Signed-off-by: Michal Čihař <michal@cihar.com>
Merge remote-tracking branch 'origin/QA_4_2'