This prevents buffering of the cache file output.

This fixes several problems:
- the CSS cache was only updated when either the CSS files for all media
  types or one of the global files was modified
- when only the screen CSS was changed, the screen CSS was regenerated
  but then the cache was printed which either caused duplicated screen
  CSS output when gzip output was disabled or invalid output with gzip
  enabled as first the plain text screen CSS and then the
  gzip-compressed cache file was printed

Now first all CSS files are collected, then the cache is checked once
and only after this the CSS content is collected.

This simplifies a while loop in the js_compress() code. The
functionality of the new code is completely identical to the old code
but it uses less comparisons and according to FS#2593 it is thus a lot
faster.

See
http://stackoverflow.com/questions/805107/how-to-create-multiline-strings
for info on them.

Instead of three stylesheets for 'all', 'screen' and 'print' modes, they are all loaded into a single stylesheet by wrapping all screen styles in a "@media screen {}" and all print styles in a "@media print {}". The 'all' mode is not wrapped in anything.
Potential issues with existing CSS: If any of your screen or print CSS files already contain any "@media" syntax, the CSS will probably break. In that case please add any CSS with "@media" in it to the 'all' mode instead!

Also, the 'rtl' mode is hereby deprecated. Please just prefix any RTL styles within your normal CSS files with "[dir=rtl]". This also fixes that RTL styles cannot be added for 'all' or 'print' modes.

This removes the cachekey parameter again and instead follows
@michitux's suggestion to trigger an event for the cache usage

The score was randomly transfered as string or as integer.
This way it will always be transfered as an integer.

The score was randomly transfered as string or as integer.
This way it will always be transfered as an integer.

Added the new error codes and categories:

--- 212	Not allowed to delete media

== 230	Media edit error
--- 231	Filename not given
--- 232 File is still referenced
--- 233	Could not delete file