#571 Open correct file for upload GEDCOM

[Phil]

When using upload GEDCOM and specifying the 'target' as a GEDCOM that already exists in PhpGedView, open the file actually copied from the upload, instead of the previously existing GEDCOM.
editconfig_gedcom.php correctly detects that the target GEDCOM for an upload is already 'in' PhpGedView. It sets a flag [actually a full file specification] to show that the upload has been 'redirected' to target.bak. uploadgedcom.php uses [the existence of] that flag to warn that the existing GEDCOM will be overwritten. However, it fails to actually use that uploaded file for validation and processing. Instead is uses the previously existing GEDCOM, validating and importing that. This patch adds a couple of test for the existence of the flag and uploaded file, opening the backup file for validation and processing, when both the flag and file exist.

[Phil]

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