Delete Version Operation does not check for use in Version Picker custom fields

Steps to Reproduce:

1. Create Version 1.0 in a project
2. Create Version Picker (Single) named "New Version"
3. Create an Issue and assign Version 1.0 to Fix Version and New Version
4. Try deleting "Version 1.0" from Project Administrator

System field behavior:

If you use versions in a Fix Version in an issue, and then attempt to delete the version in project admin, we will throw a dialog warning you that the issue is being used in a version field.

Custom field behavior:

If you create a custom field, of type Single Version Picker, then create an issue and pick a version to fill this field, and then try and delete this version from the project admin screen, we will say it is not being used anywhere.

Expected Version Picker custom field behavior:

You get the same kind of warning as when you use a system field to hold your versions. Same behaviour as system field.

Additional Affect

Database inconsistency. The value of the New Version field still exist in customfieldvalue table but it could not find any related version in projectversion table.

select * from customfieldvalue where issue=<issueid> and customfield <cfid>;