Fix for distortion happens when flipping mesh normals

Issue was caused by missing X/Y displacement components
flip when flipping the normals (flipping the normals changes
the tangent space apparently and displacement vectors need
to be modified to correspond to new space).

Reported by Jonathan Williamson in IRC.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57373 954f8c5b-7b00-dc11-b283-0030488c597c
Fix compilation error caused by recent wavelength node commit

Apparently, it's bad idea to rely on compiler to cast NULL
which is (void*)0 to int -- and in fact if i was a compiler
would also generate an error.

Further, couldn't see why we need to pass NULL or 0 th add_node,
argument value is defautl to 0 already.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57374 954f8c5b-7b00-dc11-b283-0030488c597c