New branch for working on portal clipping.

Subversion-branch: /branches/portal-branch
Subversion-revision: 1540
First (early) commit. Adds the new abstract clipping class and a struct
which will be used for P_LineOpening.

Subversion-branch: /branches/portal-branch
Subversion-revision: 1541
Added a few missing things...

Subversion-branch: /branches/portal-branch
Subversion-revision: 1542
Initial round of porting. Lots of errors still but I'm making good
headway.

Subversion-branch: /branches/portal-branch
Subversion-revision: 1543
Compile errors are gone!.... in p_doomclip.cpp anyway... But it's a
start!

Subversion-branch: /branches/portal-branch
Subversion-revision: 1544
Don't know how these files actually got into the repo... ehehe

Subversion-branch: /branches/portal-branch
Subversion-revision: 1545
Cleared the compile errors out of doomclip, maputil, and trace. Does the
project compile yet? Hell no!

Subversion-branch: /branches/portal-branch
Subversion-revision: 1546
Replaced all occurances of '#include "p_map.h"' with '#include
"p_clipen.h"'... Let the error storm begin!

Subversion-branch: /branches/portal-branch
Subversion-revision: 1547
Oh, and removed p_map.h and p_map.c from the project file.

Subversion-branch: /branches/portal-branch
Subversion-revision: 1548
Clipping engine successfully abstracted to a class. This is only the
initial phase and there are probably going to be more functions that
need to become class methods, but this is a good start! Initial demo
tests are positive (no de-syncs) and there doesn't seem to be any
performance loss... Huzah!

Subversion-branch: /branches/portal-branch
Subversion-revision: 1565
Merge from trunk

Subversion-branch: /branches/portal-branch
Subversion-revision: 1566
Found a few places where contexts were being allocated and not freed.

Subversion-branch: /branches/portal-branch
Subversion-revision: 1571
Moved P_AvoidDropoff to inside ClipEngine. Added files that will
eventually become the portal clipping code.

Subversion-branch: /branches/portal-branch
Subversion-revision: 1572
Merge from trunk

Subversion-branch: /branches/portal-branch
Subversion-revision: 1573
Whoops, I was still allocating the tracer engine on the heap... LOL I SO
SILLY

Subversion-branch: /branches/portal-branch
Subversion-revision: 1574
Merge from trunk.

Subversion-branch: /branches/portal-branch
Subversion-revision: 1764
Fixed p_pspr.cpp conflicts.

Subversion-branch: /branches/portal-branch
Subversion-revision: 1765
Merge from trunk

Subversion-branch: /branches/portal-branch
Subversion-revision: 1786
Merge from trunk

Subversion-branch: /branches/portal-branch
Subversion-revision: 1793
Merge from trunk

Subversion-branch: /branches/portal-branch
Subversion-revision: 1799