exported custom data columns header wrong and no data

Per IRC session with dlobo:

Symptoms:
1. Export of any custom data field would give "custom_xx" as the column header, where xx is the field id, and no data in the column

Additional Info:
1. If the "exportableFields All" cache key was reset by adding/deleting a custom field, the export would work as expected
2. The "exportableFields All" cache key would then be truncated to a shorter array of data by any contact edit operation, and the export column would be erroneous

Fix steps:
1. CRM/Contact/BAO/Contact.php patch by dlobo (patched copy of Contact.php from 2.2.5 release attached)
2. Alter table civicrm_cache to make `data` field longtext (allowing for more cached data for lots and lots and lots of custom fields)