rawdenoise: don't take sqrt of a negative number

(and expect real results)
(cherry picked from commit 8c67cb06d03edb1a67b6a2b6ab83c2e43531909c)
noise profile: samsung wb2000 by christer
(cherry picked from commit 4718c651f3b2bef7e3c6fbe07ad4eb064482d0fd)
noise profile: sony a99v by wiebe bierma.
(cherry picked from commit aa8f7eca9ccf792a476c46e45bd2496a8f394cdf)
noise profile: g10 by sergej nikolaev
(cherry picked from commit 789fdfc6a4c3722917b447f53efcf0d2993cf71d)
exif: don't ever use libraw to fill exif data.
(cherry picked from commit 5668c8d14362d375a92d2b2290f0dd3a06058caf)
highlights: fix some sharp borders and some magenta.
(cherry picked from commit 3b07ec4b217177250fcbbfc9b25bff58e48209d7)
wb_presets: sony slt-a37 (stolen from ufraw)
(cherry picked from commit e8a7f3f5758e0363f0be7350d5739d4ae5cbdd99)
(cherry picked from commit 948667630889344954aeccb4ac7e8961786c82f3)
opencl: don't build cltest without opencl
(cherry picked from commit 8a91e8dabfd960d56c42716765357da94d5e615b)
(cherry picked from commit 78060912101f395cbe5d34fa1d6878929ec90bee)
opencl: fix a few numerical constants in CL-sources: double -> float
(cherry picked from commit 71acf6885f46480f0216c80e2e5afbf06a6cd71e)
tiling: make maximum number of tiles a configuration parameter

users who want to process gigapixel panoramas may try to increase this value
(cherry picked from commit b431d7c7b3bac27091204f6dcabf718f8685a853)
Merge branch 'darktable-1.2.x' of github.com:darktable-org/darktable into darktable-1.2.x