Bug in File - > Save With Mark

[CsatiZoltan]

File - > Save With Mark fails on this line

imagepy/imagepy/menus/File/save_plg.py

Line 23 in 9710a27

WindowsManager.get().canvas.save_buffer(para['path'])

with the error

AttributeError: 'Canvas' object has no attribute 'save_buffer'

The same error persists both on Windows and on Linux.

[qixinbo]

You can refer to this PR to solve this problem.