Added merge driver for .dmm files.

.gitattributes

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+*.dmm merge=merge-dmm

.gitconfig

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+[merge "merge-dmm"]
+    name = mapmerge driver
+    driver = ./mapmerge.sh %O %A %B
+    recursive = text
+

mapmerge.sh

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+java -jar MapPatcher.jar -unpack $1 $1 > /dev/null
+java -jar MapPatcher.jar -unpack $2 $2 > /dev/null
+java -jar MapPatcher.jar -unpack $3 $3 > /dev/null
+
+cp $2 original.dmm
+
+echo "Map merge conflict, make sure to repack the map with MapPatcher -pack and clean it with MapPatcher -clean original.dmm"
+exit 0