[mkgmap-dev] Lower speed on highway=construction, disused=yes

This patch should omit highway=proposed from the generated maps, and it should lower the road speed of construction=* and disused=yes. The highway=construction is still translated with a different line style, but other highway=* & (construction=* | disused=yes) will use the line type of the highway=*. This is based on a suggestion by Carlos Dávila. I did not test the routing, because I have not played with road_speed before. Can someone please tell me if this is OK to commit? Marko