[CMake] FindXXX.cmake specification inconsistency

[r.koebler at yahoo.de]

> >in detail: many of these packages
> >- set XXX_INCLUDE_DIR, and put it into the cache (via FIND_PATH)
> >- set XXX_INCLUDE_DIRS to XXX_INCLUDE_DIR (if the library was found),
> >                      and don't put it into the cache.
> >- set XXX_LIBRARY,     and put it into the cache (via FIND_LIBRARY)
> >- set XXX_LIBRARIES    to XXX_LIBRARY     (if the library was found),
> >                      and don't put it into the cache.
> 
> and that behaviour is exactly consistent with readme.txt.
but what's the reason for these "duplicate" variables?

unfortunately, I cannot find any reason for this in the readme
or in this mailinglist.

regards,
Roland