Return the ELinOS environment.
If the ELinOS environment is properly set up, return a dictionary
which contains:
* The path to the ELinOS project at key 'project';
* The path to the ELinOS CDK at key 'cdk';
* The ELinOS target name at key 'target' (Eg. 'i486-linux');
* A list of Xenomai install prefixes (which could be empty, if
the ELinOS project does not include Xenomai) at key 'xenomai'.
If one of these cannot be found, print a warning; the corresponding
value in the returned dictionary will be None.