www/py-seafdav Update

[ultima1252_gmail.com]

Summary

Update for the Seahub stack.

* Updated to 5.1.0
* Changed to -pro branch to match seahub stack
* Added Max python version
* Added SHEBANGFIX to USES

Test Plan

Currently testing, and using this patch. It works better then current
version. Have created many jails and installed this port to verify working order.
Poudriere is happy on with bulk -t on 102amd64, 102i386, 93amd64, and 93i386.

[ultima1252_gmail.com]

• Added SHEBANGFIX

[miwi]

Was committed with Revision 401896.