report error if sequel can't execute

This happens e.g. if sequel is not installed and in PATH.
improve database tool execution

* Mark import_osm.sh as executable bash script.
* Use ruby from PATH in run_migrations.rb.
Merge pull request #4 from tuukka/feature/db-tool-execution

improve db tool execution
added oens data
Merge branch 'master' of https://github.com/waagsociety/citysdk
added bevolking prognose
Merge branch 'master' of gits:city_sdk
Added session expire
Reload layers every 5 min.
Now uses memcached for layer cache.
Renamed Layer.nameFromId
Added functions to ensure availability of layers in cache
Merge branch 'master' of gits:city_sdk
added oens years
Merge branch 'master' of gits:city_sdk
Added TODOs
Fixed horrible bug
Merge branch 'master' of gits:city_sdk
run some sql migrations that were not running
make gtfs import work without superuser
Merge pull request #17 from tuukka/bug/non-superuser-gtfs

make gtfs import work without superuser