Attempt to fix a potential name conflict between Freestyle and the compositor.

A crash in the Freestyle renderer was reported by Ton on IRC with a stack trace
below.  Note that #2 is in Freestyle, whereas #1 is in the compositor.  The problem
was observed in a debug build on OS X 10.7 (gcc 4.2, openmp disabled, no llvm).

----------------------------------------------------------------------
Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: 13 at address: 0x0000000000000000
[Switching to process 72386 thread 0xf303]
0x0000000100c129f3 in NodeBase::~NodeBase (this=0x10e501c80) at COM_NodeBase.cpp:43
43			delete (this->m_outputsockets.back());
Current language:  auto; currently c++
(gdb) where
#0  0x0000000100c129f3 in NodeBase::~NodeBase (this=0x10e501c80) at COM_NodeBase.cpp:43
#1  0x0000000100c29066 in Node::~Node (this=0x10e501c80) at COM_Node.h:49
#2  0x000000010089c273 in NodeShape::~NodeShape (this=0x10e501c80) at NodeShape.cpp:43
#3  0x000000010089910b in NodeGroup::destroy (this=0x10e501da0) at NodeGroup.cpp:61
#4  0x00000001008990cd in NodeGroup::destroy (this=0x10e5014b0) at NodeGroup.cpp:59
#5  0x00000001008990cd in NodeGroup::destroy (this=0x114e18da0) at NodeGroup.cpp:59
#6  0x00000001007e6602 in Controller::ClearRootNode (this=0x114e19640) at Controller.cpp:329
#7  0x00000001007ea52e in Controller::LoadMesh (this=0x114e19640, re=0x10aba4638, srl=0x1140f5258) at Controller.cpp:302
#8  0x00000001008030ad in prepare (re=0x10aba4638, srl=0x1140f5258) at FRS_freestyle.cpp:302
#9  0x000000010080457a in FRS_do_stroke_rendering (re=0x10aba4638, srl=0x1140f5258) at FRS_freestyle.cpp:600
#10 0x00000001006aeb9d in add_freestyle (re=0x10aba4638) at pipeline.c:1584
#11 0x00000001006aceb7 in do_render_3d (re=0x10aba4638) at pipeline.c:1094
#12 0x00000001006ae061 in do_render_fields_blur_3d (re=0x10aba4638) at pipeline.c:1367
#13 0x00000001006afa16 in do_render_composite_fields_blur_3d (re=0x10aba4638) at pipeline.c:1815
#14 0x00000001006b04e4 in do_render_all_options (re=0x10aba4638) at pipeline.c:2021
----------------------------------------------------------------------

Apparently a name conflict between the two Blender modules is taking place.
The present commit hence intends to address it by putting all the Freestyle C++
classes in the namespace 'Freestyle'.  This revision will also prevent potential
name conflicts with other Blender modules in the future.

Special thanks to Lukas Toenne for the help with C++ namespace.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55915 954f8c5b-7b00-dc11-b283-0030488c597c