[TYPO3-core] RFC: performance enhancement for BE

[Michael Stucki]

Hmmm. While I like the improvement of this patch, I dislike having it in
TYPO3_4-0. It is definitely a feature, may it harm or not!

Please be more strict to the rules we have set up on our own. We did so
because we want to make a promise to our users:

Patch versions do _never_ cause any problems!

I truely believe Dmitry and everybody else that this patch worked fine on
their system, but still there is a small chance that this could case
trouble on a system. After all, that's not what we want to risk because
this is not the reason why we intended the patch level versions.

Please Dmitry, revert this for TYPO3_4-0.

- michael

PS: Two more comments about the change as such:
- Since .htaccess files affect subdirectories recursively, I think that
  one .htaccess in typo3/ would be good enough.
- Some of the files contained Windows line breaks. Please remove them.

> Problem: BE has many images. They are static (not changing). Default
> installation does nothing to cache them on the client side. This puts
> caching task to the browser (== to check if image is modified and reload
> it if necessary). At least MSIE does this badly - it always reloads
> every image in the BE causing a lot more traffic than necessary and
> taking resources from httpd process.
> 
> Solution: put .htaccess files to several places to the BE with special
> instructions to cache images and css from t3skin. Exact places are:
> - typo3/gfx (all BE default icons)
> - sysext (mainly impacts t3skin and rtehtmlarea - huge improvement in
> rte loading time!)
> - sysext/t3skin/stylesheets (caches only styles)
> All .htaccess files define FileETag to MTime+size which is good enough
> and works on all file systems. They also check if mod_expires installed
> and set expiration of cache to 7 days from the current time. This will
> cause "If-modified-since" header from the browser and "Not modified"
> response from the server, which is much faster than normal
> request/response.
> 
> This patch is tested for a couple of weeks in the installation with
> several editors. No one complained but people said that BE works faster
> now.
> 
> Patch is attached.
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