[release] Honor USE_CMAKE environment variable and allow deactivating it on the command line.

With this patch the USE_CMAKE environment variable is queried whether or not CMake
should be used. This can be overwritten in an options file or on the command line
using either the --cmake or --no-cmakr switch.

bin/dunecontrol

@@ -795,6 +795,9 @@ export RESUME_FLAG=no
 export REVERSE_FLAG=no
 export SKIPFIRST=no
 
+# read environment variable USE_CMAKE
+export DUNE_USE_CMAKE="$(echo $USE_CMAKE)"
+
 # parse commandline parameters
 while test $# -gt 0; do
     # get option
@@ -902,9 +905,12 @@ while test $# -gt 0; do
     --skipfirst)
       export SKIPFIRST=yes
     ;;
-    --use-cmake)
+    --use-cmake|--cmake)
       export DUNE_USE_CMAKE=yes
     ;;
+    --no-cmake)
+      export DUNE_USE_CMAKE=no
+    ;;
     --debug) true ;; # ignore this option, it is handled right at the beginning
     --*)
       usage