Time to merge the pgoyette-compat branch

[Paul Goyette <paul%whooppee.com@localhost>]

Folks,

After several months of work, it's now (nearly) time to merge the
pgoyette-compat branch.  (Yeah, I know that many/most of you don't
"allow" modules into your environments in the first place, so none
of this really affects you at all.)


This branch includes the following major changes:

* Separation of the single "monolithic" compat module into multiple
  modules, one for each older version of NetBSD.

  With this, you can load only as much compat code as you want, without
  having to build a custom compat module.  (You still need a custom
  kernel to start with, in order not to have all the compat code being
  built-in.)  Sys-calls that are implemented in the compat module will
  now load only the necessary compat code, rather than the entire
  monolithic module.

* Introduction of module "aliases".  In addition to its own name, a
  module can now provide alias names.  This is useful for the
  monolithic compat module, which now contains the functionality of
  the many version-specific modules.  If you load the monolithic module,
  its aliases will prevent you from also loading individual-version
  compat modules.

* Elimination of the limit on the number of "required" modules (or
  "dependencies") for a module.  There was previously a limit of
  MAXMODDEPS (value 10), with a statically-allocated array;  now the
  array is dynamically allocated and expanded as needed.

* Extraction of some COMPAT_xx code that was previously intertwined
  with the main kernel build and not available in non-built-in modules.
  One example of this is the COMPAT_70 code for rtsock (which bit me
  when it was introduced, and was the main reason for undertaking the
  work on this branch).

* Removed linking of the .o kernel compat library into all kernels.
  This caused problems, since the library included lots of compat
  symbols, but did not include module linkage; attempts to subsequently
  load some modules would fail due to multiply-defined symbols.

* Reverting of some previous intentionally-introduced breakage in the
  sysv_ipc module.  (The breakage was introduced to work-around the
  above compat library issue.)

Other activity is documented in src/doc/COMPAT-branch-notes file.

There are a number of activities that still need to be worked on;  these
are also listed in the src/doc/COMPAT-branch-notes file.  None of these
activites should prevent merging of the branch, as the short-comings are
already present on the mainline.

I welcome any timely review and constructive feedback.  I'd like to get
this committed sometime in the next two or three weeks if possible.


+------------------+--------------------------+----------------------------+
| Paul Goyette     | PGP Key fingerprint:     | E-mail addresses:          |
| (Retired)        | FA29 0E3B 35AF E8AE 6651 | paul at whooppee dot com   |
| Kernel Developer | 0786 F758 55DE 53BA 7731 | pgoyette at netbsd dot org |
+------------------+--------------------------+----------------------------+