Garfield compilation fix

[jgalan]

CMakeLists fixes related to Garfield compilation of old versions.

Related to #37

[lobis]

The changes are fine (I took the opportunity to make some formatting changes and remove old comments).

However it doesn't make sense that this file suddenly stops working, there must be a problem with the sultan installation of Garfield I think. For example, at /programas/garfield/6.24.02 there are two "includes", one include and one Include, something must be wrong.

I would reinstall the same version of Garfield and check if this PR is really needed before merging.

Or just install the latest Garfield version and work with that, and probably drop support for old Garfield altogether, which will save time on the long run I think.

[jgalan]

The good one is include, it is the one generated by the installation. Include is the one from the sources. Both should have the same content anyway. This happens because the install path is defined as GARFIELD_HOME. I believe this is because it was like that at the original installation instructions of Garfield.

The changes happening at this PR had no effect on solving my compilation problem. The problem was solved at detectorlib. The reason behind is that the include directories were not the right ones.