Makefile: fix build on OSX

Override LANG things to make it build on OSX
Makefile: use $(AT) to enable V=1 in make
Makefile: --in-place isn't supported, option is -i

Note that -i takes a mandatory parameter, which is the backup extension.
We don't use that, so it's just empty.
dev_scripts: remove GNU readlink usage

Revert to old "cd && pwd" trick as it works reliably enough.
(hint, target is a directory, not a file)
Port the dev_scripts to OSX

This ports the various dev tools to OSX. It removes some GNU specifics,
and might be very useful on other *BSD as well.
Fix the chown correctly

Previous commit did just remove the chown in the Makefile. This is
obviously wrong.

Now we just override the $(CHOWN) to be /bin/true, which will do what is
epxected when using dev_script/install.
dev_scripts: overriding various USER in script

The USER vars are overriden directly when invoking make instead of
hardwiring them into Makefile.config. This avoid changing the normal
build system, and localize changes into the dev_scripts/ subdir
Merge pull request #254 from steveschnepp/osx

Port the development environnement to OSX