[duneproject] Update CMake minimum version if ENABLE_ALL is true

dune_enable_all_packages() now requires CMake 2.8.12, so make sure
duneproject generates a correct template.

Also output a warning to tell the user about this change in required
CMake version.

bin/duneproject

@@ -182,6 +182,9 @@ DEPENDENCIES="$2"
 VERSION="$3"
 MAINTAINER="$4"
 
+# Track minimum CMake version
+CMAKE_MINIMUM_REQUIRED=2.8.6
+
 ################## READ OPTIONS ##################
 
 while [ "$DATACORRECT" != "y" -a "$DATACORRECT" != "Y" ]; do
@@ -226,7 +229,8 @@ while [ "$DATACORRECT" != "y" -a "$DATACORRECT" != "Y" ]; do
     read -p "4) Maintainer's email address? " MAINTAINER
   done
   while [ "$ENABLE_ALL" != "y" -a "$ENABLE_ALL" != "Y" -a "$ENABLE_ALL" != "n" -a "$ENABLE_ALL" != "N" ]; do
-    read -p "5) Enable all available packages? (Choose 'y' if you don't understand the question.) [y/N]" ENABLE_ALL
+    echo "5) Enable all available packages? (Choose 'y' if you don't understand the question, but see warning below.)"
+    read -p "   WARNING: If you enable this option, your module will require at least CMake 2.8.12 to build. You can check your version with 'cmake --version' [y/N]" ENABLE_ALL
   done
 
   echo
@@ -243,11 +247,17 @@ while [ "$DATACORRECT" != "y" -a "$DATACORRECT" != "Y" ]; do
     MAINTAINER=""
     ENABLE_ALL=""
   fi
+
 done
 
 # canonicalize contents of ENABLE_ALL
 ENABLE_ALL=$(tr '[:upper:]' '[:lower:]' <<< "$ENABLE_ALL")
 
+# set newer CMake minimum version if ENABLE_ALL is true
+if [ 'y' == "$ENABLE_ALL" ] ; then
+  CMAKE_MINIMUM_REQUIRED=2.8.12
+fi
+
 
 echo
 echo "A sample code $MODULE.cc is generated in the \"$PROJECT\" directory."
@@ -377,7 +387,7 @@ Preparing the Sources
 Additional to the software mentioned in README you'll need the
 following programs installed on your system:
 
-  cmake >= 2.8.6
+  cmake >= ${CMAKE_MINIMUM_REQUIRED}
 
 or if you use the old autoconf build system:
 
@@ -490,7 +500,7 @@ M_DELIM
 ################## CMakeLists.txt ##################
 echo "- $PROJECT/CMakeLists.txt"
 cat> "$PROJECT/CMakeLists.txt" << M_DELIM
-cmake_minimum_required(VERSION 2.8.6)
+cmake_minimum_required(VERSION ${CMAKE_MINIMUM_REQUIRED})
 project($PROJECT CXX)
 
 if(NOT (dune-common_DIR OR dune-common_ROOT OR