Refactor engines handling in configure script
After seeing the added "Engines Skipped" listing, it made me think about the current hardcoded handling of engines in the configure script.
The attached patch refactors it so all the information about an engine is compacted in a small array of variables and then this information is used wherever it's needed in a generalized way.
This could also be used to dynamically generate the engine information in engines/engines.mk and base/plugins.cpp, but I remember Fingolfin said some ports don't use the configure script... Maybe the engine information could be extracted outside the configure script to make it even more general? If there's interest on this I could try to work on it.
Again, this eases the maintenance of out-of-trunk engines, having just to mantain the engine information array.
This approach uses evaluation of variables with dynamic names. I've tried it with bash and busybox's ash, but I don't know if I'm using some shell specifics that could cause troubles in other shells and reduce portability.
Ticket imported from: #1822349. Ticket imported from: patches/840.