Avoid browser cache (Return code 304 Not Modified)

[rristow]

If the "plone.app.caching" is configured to cache the images, the image will not be updated in the browser (return code=304 not modified).

steps to reproduce:

• go to @@caching-controlpanel/caching operations
• set "File and image resources" caching to moderate or strong
• go to @@croppingeditor and crop the image
• After saving the "new" image will not be update in the browser (return code 304). The user can still force the update with CTRL+F5 Firefox)

[frisi]

thanks for pointing this out @rristow !

personally i'd call setModificationDate() after saving the crop since this is what actually modifies the image.

not sure if this leads to the same problem as we have in #21?
if the anwer is yes, then this change will delete all other cropped scales except the current one.

i think we should add a testcase that makes sure existing cropped scales are still cropped after cropping another scale.

[tomgross]

It does lead to the same problem as in #21

[tomgross]

This is superseeded by pull request #38