On copyNode, make useful srcWorkspace

Hello,

I changed pathExists to perform the test on a specific workspace. 
I changed copyNode for the srcWorkspace option is useful.

Best regards,
On copyNode, make useful srcWorkspace

Correction based on dbu's and lsmith77's advice.
Update Client.php

Typo fixed.
Merge pull request #197 from ApiciusPoulet/patch-1

On copyNode, make useful srcWorkspace