HEADSUP: drm-current-kmod now installs sources

With help from zeising_at_ in particular, I've just committed a change
to the drm-current-kmod port that makes it install sources into
/usr/local/sys/modules by default.  This will result in some behavior
changes on HEAD (and only head for now):

1) When you build a kernel after installing the updated package,
   your buildkernel will now build DRM modules using the sources
   from the package.  For developers at least I suspect this to be
   a win as if you have made changes to the kernel KBI you will
   always end up with matching modules installed into /boot/kernel
   alongside your kernel.

2) In order to use these modules, you need to update the 'kld_list'
   lines in your rc.conf to just list the modules without a
   path, e.g. "kld_list=i915kms" just as you would for other
   modules.  This will prefer the module built with your kernel if
   one exists and fall back to the module in /boot/modules
   otherwise.

If a change in current breaks the build of DRM modules, you have a
couple of options:

1) Pass 'LOCAL_MODULES=' (empty string) on the command line of
   'make buildkernel' to disable building the DRM modules.

2) Hack on the sources in /usr/local/sys/modules/drm-current-kmod
   to fix the compile breakage, perhaps using a patch from the
   mailing lists if one exists.

3) Wait for a new package/port version and update to that before
   doing a buildkernel.

For developers this means even if you are doing testing on a box
that doesn't use DRM, you can install the package so that kernel
builds will try to compile it and hopefully spot KPI/KBI changes
before they land in the tree so that the port/package can be
patched in tandem with committing changes to HEAD.  Note that even
builds of work trees in git checkouts, etc. will find the DRM
modules and try to build them if the package is installed.

-- 
John Baldwin