nobase_ room for improvement

[Robert Collins]

Just an idea.

I use automake to make non-recursive build environments fairly routinely
now. (Recursive-make-considered-bad ...)

Installation of headers in subdirectories is more complex than it could
be (IMO).

The nobase_ prefix allows utilising an existing directory tree, but a
non-recursive build will almost always have a directory or two below the
Makefile that aren't desired on install.

While defining a new target to be $(includedir)/foo lets you work around
this, it would be great to do something like:

nobase_preserve_foo_HEADERS = ...

and have it achieve the same result.

Anyway, just some food for thought.

Cheers,
Rob