Fix postgis installation on travis CI
Merge branch 'branch-6-4'

Conflicts:
	.travis.yml
Switch free to msFree in filter translation function.
Merge branch 'master' of https://github.com/mapserver/mapserver into rfc91-filter-transform
Switch WFS dwithin/beyond filter creation to compute a distance in layer units rather than buffering.
Merge branch 'rfc91-filter-transform' of https://github.com/sdlime/mapserver into rfc91-filter-transform
Correct unit handling for dwithin/beyond cases