Bug in line number determination for validations of repeating metadata entries

[jannahastings]

The line number determination seems to fail sometimes, in the validations, when there is more than one entry of the same type.

Two scenarios that can reproducibly cause problems are:

1. when there is more than one entry of the same type in a repeat (e.g. in the PURL schema there can be several redirections specified), and the error occurs in the second or subsequent entry, the line number returned is for the first entry

2. when an error has occurred in an entry, is validated and repaired, but then another error is introduced in an entry of the same type but at a different line, the line number returned for the error is for the original error line