Add cr2hdr.lua script.

This script automates the steps involved to process an image created
with the Magic Lantern Dual ISO module. Upon invoking the script with a
shortcut "cr2hdr" provided by Magic Lantern is run on the selected
images. The processed files are imported. They are also made group
leaders to hide the original files.

contrib/cr2hdr.lua

@@ -0,0 +1,79 @@
+--[[
+    Copyright (C) 2015 Till Theato <theato@ttill.de>.
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+]]
+--[[
+cr2hdr …
+
+This script …
+
+USAGE
+* require this script from your main lua file
+* …
+]]
+
+local darktable = require "darktable"
+
+-- Tested with darktable 1.6.2
+darktable.configuration.check_version(...,{2,0,2})
+
+local processed_files = {}
+
+function file_imported(event, image)
+    local filename = image.path .. "/" .. image.filename
+    if processed_files[filename] then
+        image.make_group_leader(image)
+        processed_files[filename] = nil
+    end
+end
+
+-- Source: http://lua-users.org/wiki/SplitJoin
+function lines(str)
+  local t = {}
+  local function helper(line) table.insert(t, line) return "" end
+  helper((str:gsub("(.-)\r?\n", helper)))
+  return t
+end
+
+function convert_image(image)
+    if string.sub(image.filename, -3) == "CR2" then
+        local filename = image.path .. "/" .. image.filename
+        local handle = io.popen("cr2hdr " .. filename)
+        local result = handle:read("*a")
+        handle:close()
+        local out_filename = string.gsub(filename, ".CR2", ".DNG")
+        local file = io.open(out_filename)
+        if file then
+            file:close()
+            processed_files[out_filename] = true
+            darktable.database.import(out_filename)
+        else
+            result = lines(result)
+            darktable.print_error(image.filename .. ": cr2hdr failed: " .. result[#result-1])
+        end
+    else
+        darktable.print_error(image.filename .. " is not a Canon RAW.")
+    end
+end
+
+function convert_action_images(shortcut)
+    local images = darktable.gui.action_images
+    for _,image in pairs(images) do
+        convert_image(image)
+    end
+end
+
+darktable.register_event("shortcut", convert_action_images, "Run cr2hdr (Magic Lantern DualISO converter) on ... images")
+darktable.register_event("post-import-image", file_imported)