Fix PHP Fatal error: Undefined class constant 'ERROR_FORBIDDEN' (T2253)
Summary: Fixes T2253
Test Plan:
With enabled WebDAV browser upload the same file twice to the same folder.
Second try should return proper exception status instead of a white page.
Reviewers: iRony Developers
Maniphest Tasks: T2253
Differential Revision: https://git.kolab.org/D384