added set_alias function
added modextraalias var to easyconfig/default.py
use modextraalias in easyblock.py
added unit test for test_alias
rename modextraalias to modaliases
Merge pull request #6 from boegel/add-alias

rename modextraalias to modaliases
Merge branch 'develop' of https://github.com/hpcugent/easybuild-framework into add-alias
Merge branch 'add-alias' of https://github.com/pescobar/easybuild-framework into add-alias
Merge pull request #952 from pescobar/add-alias

define alias for the modulefile in your easyconfigs