Reuse WSF_LAUNCHABLE_SERVICE code as ancestor of WSF_DEFAULT_SERVICE_I
Note that this way, it is easy to redefine `launch' in order to customize the launching instruction if needed (thinking about testing...)
This might breaks some code since it adds a `launch' feature, but it is easy to fix and unlikely to happen often.
Merge branch 'master' of https://github.com/EiffelWebFramework/EWF
Removed unused local variables.
Added WSF_REQUEST.has_execution_variable (a_name): BOOLEAN
Since the related value can be Void.
removed unused local variable