Adding rawPixelDataToBuffer() function for access to compressed data read from scanline input files.

Changes from The Foundry to add rawPixelDataToBuffer(...) function to the OpenEXR library. This allows you to read raw scan lines into an external buffer. It's similar to the existing function rawPixelData, but unlike this existing function it allows the user to control where the data will be stored instead of reading it into a local buffer. This means you can store multiple raw scan lines at once and enables the decompression of these scan lines to be done in parallel using an application's own threads.
(cherry picked from commit ca76ebb40a3c5a5c8e055f0c8d8be03ca52e91c8)