With attachments stored on disk, if the project's upload directory
changes and the files are moved to the new location, it is no longer
possible to clone issues.

The file_copy_attachments() function was modified to use the same logic
as elsewhere in MantisBT, i.e. rely on file_normalize_attachment_path()
to determine the attachment's path.

Fixes #14718

Prior to this, the upload path would not be checked if it was empty
(ie. defaulting to $g_absolute_path_default_upload_folder),
which could cause issues if that directory was missing or read-only.

Checking this early allows catching any errors before users perform
actual operations on file attachments.

Fixes #14723

The logic implemented in 7aa07d8 for
manage_proj_edit_page.php also applies to manage_proj_create_page.php.

Fixes #14700

config_get() would return the file upload method for the current
project, instead of the one for the project being edited.

Use of $g_project_override for expected behavior.

Fixes #14700

The following changes were made:

 - Display the fields in the same order
 - Make the fields identical length
 - Display the "required" star next to project name
 - Use identical variable names

Fixes #14725

Fixes #14724, affects #14700

Revised code so that generated page complies with xhtml 1.0 strict DTD.