Elevation feature

Since last pull request, lots of code was removed and tests reworked:
- The Phantom node elevation is computed earlier (patch from @radupopescu;
- Test code is reworked to use valuable suggestions by @emiltin.

The pull request was split in two parts:
- small fixes unrelated to elevation feature (https://github.com/DennisOSRM/Project-OSRM/pull/1094);
- elevation feature, with tests.


Regarding https://github.com/DennisOSRM/Project-OSRM/pull/1089#issuecomment-46652889,
an open discussion would certainly ease mutual understanding and lead to solutions.

The code looks good now and would probably be of use for others.
I found out these project which try to enhance OSM data using SRTM elevations:
- https://code.google.com/p/osmosis-srtm-plugin/ a plugin for osmosis;
- http://wiki.openstreetmap.org/wiki/Srtm2wayinfo .

Regards,