Last patch reviewed.

[Ramón García]

Although the deadline passed some hours ago, I am resending the last
patch to fix some issues with the documentation. There are no changes
in the code.

As I mentioned in the last post, these patches implement a new
feature: a flag "not-inherit" for variables target or pattern
specific. This flag prevent a variable from being transmitted from a
target to its prerequisites.

The code delivered passes all current tests, except some
non-reproducible failures in targets/SECONDARY (it happens randomly).
I am investigating this issue.

Ramon