Actually fix request #5554: Cannot select CSV preference in use prefs page

This is a tricky one.
TL;DR: autoload should not be used to load "automagically" old src/www/include
stuff because variables will not be defined.

Long story, you shall take pop corn:
Long time ago, "standards" said that it was great to define variables (like
csv_separators) in files like utils.php and to reuse this variable wherever
needed. Due to some require magic (dependency hell), it was available anywhere.

Fast forward to 6.7 release, we try to autoload anything of core.
So, utils.php is still loaded by some require magic (here its through tracker
date reminder plugin and tracker v3) but it's not longer an explicit require,
on plugin init, it's made though a function call (autoload is a function) so
utils.php is loaded in a function too.
Consequence: csv_separator is defined in a function, when the function ends,
it's no longer defined.

Not a problem you say, "let's require utils.php explicitly where I needed it"!
Not that simple padawan, if you require_once utils.php after pre.php, php will
tell ya "utils.php" is already loaded, skip it => GTFO!

So, the only valid way to fix that is to:
- avoid usage of shared variables (should be const or functions)
- otherwise avoid magic inclusions (it's the purpose of this commit).

That's all folks!

Change-Id: I876646d9aeb4b37c90acaf4c25120398e9502629
Merge commit 'refs/changes/28/1428/1' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  Actually fix request #5554: Cannot select CSV preference in use prefs page

Change-Id: I100724f0a6897c6eb880634223ccbef560eaeaa1
This is Tuleap 6.7.99.1

Change-Id: Icf1e41e1e67b8434d83f5215c4c3160192e6deda