[TYPO3-core] RFC #16611: Bug: [scheduler] tx_scheduler_CronCmd needs refactoring

[Christian Kuhn]

This is an SVN patch request.

Type: bugfix

Branches: trunk

BT: http://bugs.typo3.org/view.php?id=16611

Problem:
The scheduler cron command parser complex, hard to unterstand and still 
has several bugs.

Solution:
Rewrite from scratch.

Notes:
- The new code has very high unit test code coverage, we're now counting 
286 assertions for this extension.
- This patch introduces a new class which 'normalizes' a given cron 
command. The class implements the full cron command syntax as documented 
eg. in vixiecron. Take a look at the unit tests to see what is possible.
- The cron command normalizer throws exceptions if something is wrong 
with the command. So it can be easily used in the scheduler backend to 
validate a command (with another RFC).
- After the cron command normalizer was successfully run, the cron 
command just consists of a list of comma separated integers or the 
character '*' for each field.
- The CronCmd class itself, and especially the recursive method
calculateNextValue() was rewritten and is now much more simple to 
understand and should be pretty easy to maintain. The strategy is to 
increment the given timestamp until all cron command restrictions match.
- As you might guess, this took me quite some hours to get it right. I'm 
pretty sure all important things are ok, even things like a cron command 
timed on every leap year is handled. Still, even with so many unit tests 
I'm not 100% sure it's bugfree.

Regards
Christian
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