CRM-19250 breaks saved search

Hi!

Since CRM-19250 was fixed, it breaks all relative dates if the user changed the default date input field.

To reproduce this issue, change the default “Date Input Format” to “dd/mm/yyyy” and then
update any cached group that is based on a relative dates. This will break all that saved search by using a false SQL date (`19700101000000`).

The issue comes from PHP’s `strtotime()` that can’t convert the localized date to an epoch (in `CRM_Utils_Date::processDate()`). I don’t know if we could use the user’s configuration in that `processDate()` function.

In the meantime, reverting CRM-19250 solves the problem.

Cheers,
Olivier;