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
Added build files for VS2012.

The solution files were imported from the VS2012; a few fixes
were needed: the $(WindowsSdkDir) no longer points to the correct
paths. The relevant variables are $(WindowsSDK_IncludePath),
$(WindowsSDK_LibraryPath_x64) and $(WindowsSDK_LibraryPath_x86).
Modified .gitignore to ignore Visual Studio stuff

Added intellisense files, user property files and VS build folders
Merge pull request #14 from TheEpsylon/master

Build files for VS2012 + relevant .gitignore changes.