The pgxs makefile in Postgres <= 9.2 cannot yet handle VPATH
correctly. Provide header paths explicitly and overwrite
VPATH after sourcing the pgxs file.
Fixes#454.
Some postgres installations report problems with the makefile
magic that should look for the source where the Makefile is
located. So hand in the path explicitly via VPATH instead.
Fixes#453.
- move the configure from nominatim out and add checks for all dependencies
- bring module under automake control
- add osm2pgsql as a submodule, configure and build with the others