[Tagging] default value for "oneway"

[Xavier Noria]

Since I see the characteristics of Barcelona (and other cities/towns I
know) are exceptional for most of you guys, let me share a couple of
maps to explain where I am coming from.

This is a typical sector of Barcelona:

     https://www.dropbox.com/s/k7o32zbneoi8y6q/barcelona_sample.png?dl=0

As you see, almost everything is one-way. Of course there are some
important streets here and there that are two-way, but the ratio is
really small.

So for example, in this map from OSM that has streets with no oneway
set highlighted in blue:

    https://www.dropbox.com/s/yjosl8lwyk3xkme/barcelona_bad_sector.png?dl=0

that area in the center with many blue lines... almost all of them are
wrong. You cannot rely on that default in Barcelona at all.