opencl: fix efficacy bug in globaltonemap
Merge branch 'master' into opencl
opencl: give numbers and names of available OpenCL devices as part of debug output

this is the first step to make darktable deal more flexible with multiple GPUs
opencl: add module flag to prevent preview pixelpipe processing on GPU
opencl: add colorpicker functionality to opencl pixelpipe
Merge branch 'master' into opencl
opencl: basic setup for device priority lists (individual for all pixelpipe types)
opencl: priority settings for multi-GPU systems

if you have more than one GPU you can now give priorities on how
these are allocated to the different pixelpipes
Merge branch 'master' into opencl
Merge branch 'master' into opencl
opencl, usermanual: add section about multiple OpenCL devices
opencl: alphanumeric device names in opencl_device_priority
Merge branch 'master' into opencl