Get date popup working in node author section and fix validation and form_set_value code to work right in Drupal 6.

Remove database timezone handling by rolling back to previous version that used offsets instead. Based on problems noted in #218479 and #220663, we cannot count on database timezone handling to be available in MYSQL or work consistently with the timezone names that PHP uses in POSTGRES, so trying to do timezone conversions in the database is not going to work.

Synch with D5.2 version.

#218479 Add more information about db timezone support to the INSTALL.txt file and move the requirements test to the Date Timezone module.

#209189 Move the adding of date.css from Date Timezone to Date API so it is always available. Add dependency on Date Timezone to Date Popup so timezone conversions will work.

Standardize on date_make_date() instead of calling date_create() in some places so there is a central place to test the timezone and date values before creating the date.

Add method to customize the labeling of date parts to allow the label above the date part, inserted as the first item in the options array, or omitted.

Remove some functions that are not being used or move them so they are called only when needed to clean up the code.

Consolidate date elements into a single '#date_settings' array to not pollute the form. Add in a widget settings option to show the date repeat form on the node. The repeat form doesn't actually do anything yet!

Now that this is a module, I have to watch my function names. Renaming so they don't get confused with hooks.

Move override of site and user timezone setting into its own module so it can be turned on or off and removed once this is done by core. Also make PHP4 handling into a module instead of an include file so it can be turned on or off and removed once core no longer supports PHP4.