=cloth collisions=

Plugged the eltopo library into the cloth solver.
I was playing with it earlier, and it's so easy to
use I decided to quickly put it in (trunk's) cloth.

See http://www.cs.ubc.ca/labs/imager/tr/2009/eltopo/eltopo.html
.  The authors are on the bleeding edge of continuous collision
detection (one of them did ILM's cloth sim).  
I
don't really have to time to plug it into softbody, particles,
bullet, fluid, etc, but doing so would be pretty straightforward.
I'll leave that up to someone else.

To use, turn on USE_ELTOPO (in cmake) or WITH_BF_ELTOPO in scons.

extern/CMakeLists.txt

@@ -31,6 +31,10 @@ if(WITH_BULLET)
 	add_subdirectory(bullet2)
 endif()
 
+if(WITH_ELTOPO)
+	add_subdirectory(eltopo)
+endif()
+
 if(WITH_BINRELOC)
 	add_subdirectory(binreloc)
 endif()

extern/SConscript

@@ -4,6 +4,9 @@ Import('env')
 
 SConscript(['glew/SConscript'])
 
+if env['WITH_BF_ELTOPO']:
+    SConscript(['eltopo/SConscript'])
+
 if env['WITH_BF_BULLET']:
     SConscript(['bullet2/src/SConscript'])