Plasma panel and Kephal

[todd rme]

Plasma's panel depends on "kephal/screens.h" to build.  However, this
is not header is not exported during building.  This means, unless you
have a KDE source tree on-hand, you cannot buld the panel.  This is
fine if you are just trying to build the default panel, since you
wouldn't do that out of the normal source tree.

The problem becomes when someone wants to work on a third-party panel
based on the default panel.  They can't do it without first reworking
the parts the depend on kephal, and it is not immediately obvious how
you would do so.

I think if the goal is to have people working on their own versions
that implement niche features, which has been the justification for
rejecting a number of bugs and patches in various parts of plasma,
then I think these sorts of barriers to entry serve as a strong
discouragement to people who otherwise would want to make a slight
variation on the existing panel.  I think it would be worthwhile if
all plasma containments and applets were designed in such a way that
they could easily be built from outside the KDE source tree as long as
the appropriate development packages are installed.  This will make it
much easier for people to jump in and start making their own variants
of the software.  Headers needed to build these components should
either be public or should be changed to something that is.

-Todd