Fix bug in time sample calculation.

Previously, we were twice Lerp()ing the original [0,1] sample value
from the shutter open to the shutter close time, which was the right
thing only when the frame time was from 0 to 1.

Bug reported by joelkronander@gmail.com.
Fix Makefile build of exrtotiff
Add: CMake project struct for pbrt. (Based on the scon script and vc2010.sln)
Add: code in renderer create function to include my cuda renderer
Fix: add a ifndef guard before define NOMINMAX, because the cuda CMake macro will also define that macro on commandline
Add: add the head files under core dir into CMake. (for show them in the visual studio)
Add: a global option to indicate using cuda render
Add: move construction to Shape
Add: move construction to trianglemesh
Add: release funtion to pbrt Reference. To call the relase, the reference count must be 1 and the method is not thread safe
Fix: add top level folder into include search path(to add cuda render header)
Add: a command option to force usage of cuda render
Add: hook in the cuda render
Add: object instance cuda hook
Add: friend to disk shape
Add friend declear in pbrt light, so that my code can access private member
Add friend declear to shape
Add: friend declear in kdtree to support photonmapping
Add: even more friend declear to let my code to access internal state