[Open-transport] SBB - HAFAS --> GTFS Conversion

[Christian Helbling]

> As you may have observed the 'unique key' per Z-line isn't unique either (because is unique in combination with the bitfeld), but must be unique for GTFS, hence requires a new id.
>
I woudn't be too sure that it will stay unique with *Z-line and bitfield.
I was told from SBB that one should add the '*I RN'-line to the *Z-line for uniqueness.

But to be absolutely sure you can also just add some "_".($seen[$zline]++) (php syntax) at the end.
This way you can also generate ids for frequency based connections.

-Christian