[runtime] Fix warnings.
[runtime] Remove NO_FINALIZATION.

Replace with check for Boehm where appropriate. In this runtime,
we don't yet support finalization when using Boehm.
[runtime] Defining GC_LINUX_THREADS is redundant.

Via configure, we already pass in -DGC_THREADS which will do
the right thing (and works for all platforms).

We also don't need a Boehm define when using MPS.
[runtime] Add missing platforms.
[runtime] Support building multiple runtimes.

The Makefile now supports building multiple runtimes
for each platform. The runtimes other than HARP are
not yet implemented, so we only build HARP on the
platforms where we use this directory.
[runtime] Remove obsolete function.

dylan_mm_deregister_thread was replaced a long time ago.
[runtime] Split boehm and MPS code up.
[runtime] Separate boehm/mps collector includes.

Building collector.c with Boehm no longer needs MPS includes. This
isn't all as clean as it might be, but we'll get there. There are
also other dependencies on MPS in other files still.
[runtime][boehm] Use macros for GC_MALLOC/FREE.
[runtime] Fix some typos.
[runtime] Clean up formatting of if/else/for/while.
Merge pull request #392 from waywardmonkeys/default-to-pellesc

[win32 installer] Default to PellesC.
Make <cpl-differ> a program-warning, rather than a serious-program-warning

Since 2012.1 is released, we have a release where the CPL difference
between DRM and C3 is a serious. According to discussions on hackers@
(especially https://lists.opendylan.org/pipermail/hackers/2011-December/006279.html)
we should remove the warning.

My plan is to ship next release with a warning, and afterwards
remove that entirely
Merge pull request #393 from hannesm/c3-serious-into-warning

Make <cpl-differ> a program-warning, rather than a serious-program-warni...
Remove unneeded binary file
Merge pull request #395 from hannesm/remove_bin_file

Remove unneeded binary file
[doc] Improve documentation of join generic function and method
Merge pull request #396 from abeaumont/documentation-join

[doc] Improve documentation of join generic function and method
[doc] Documentation fixes in join generic function and method pointed by @cgay
Merge pull request #397 from abeaumont/documentation-join

[doc] Documentation fixes in join generic function and method pointed by @cgay