[TYPO3-core] RFC #11430: Use $_SERVER['REQUEST_TIME'] instead of time() where it makes sense

[Niels Pardon]

This is an SVN patch request.

Type: New feature/Code cleanup

Bugtracker references:
http://bugs.typo3.org/view.php?id=11430

Branches:
trunk

Problem:
There are a lot calls to time() spread all over the core. According to
[1] calls to time() are expensive and should be avoided if possible. [1]
suggests to use $_SERVER['REQUEST_TIME'] instead.

Solution:
Use $_SERVER['REQUEST_TIME'] in config_default.php to set
$GLOBALS['EXEC_TIME'] and use $GLOBALS['SIM_EXEC_TIME'] in the other
places in the core.

Notes:
I left out 3rd party libraries like OpenID or AdoDB.

[1] http://ilia.ws/files/phptek2007_performance.pdf