Handle duplicate source, target datum references for geodetic transformations tolerant

[steffen]

When in the dictionary exist two geodetic transformations with the identical source, target datum references handle it tolerant. Select one to use. This makes it possible to execute any transformations even when the dictionary is not totally clean.

Which definition will be used when two geodetic transformations with the identical source, target datum references exists? Use the first one in the index. As the user defined definitions comes first it is expected that the user definitions are used primarily. This selection could also be enhanced in a later step, like to use the accuracy value to detect which one to use.

It is not expected to keep redundant geodetic transformations with the identical source, target datum references in the dictionaries. But by mistake redundant definitions could come in. E.g. the use case when a definition exists in the user defined dictionary and an identical system one comes with a system update. Or when a user creates a geodetic transformation with the identical source, target datum references by mistake.

[steffen]

Changeset 2422