Improve behaviour if md5sum is not installed.

install

@@ -98,7 +98,8 @@ check_afp_entries() {
         if curl -s -L $AFP_URL | tar zxf - -C .afp $extract; then 
             for e in $missing; do 
                 echo "           Registering $e in $ISABELLE_HOME_USER/ROOTS"
-		grep -q $PWD/.afp/afp-2018-08-14/thys/$e || echo "$PWD/.afp/afp-2018-08-14/thys/$e" >> $ISABELLE_HOME_USER/ROOTS 
+		touch $ISABELLE_HOME_USER/ROOTS
+		grep -q $PWD/.afp/afp-2018-08-14/thys/$e $ISABELLE_HOME_USER/ROOTS || echo "$PWD/.afp/afp-2018-08-14/thys/$e" >> $ISABELLE_HOME_USER/ROOTS 
             done
             echo "           AFP installation successful."
         else
@@ -116,14 +117,16 @@ check_isa_dof_patch() {
     echo "* Check availabilty of Isabelle/DOF patch:"
     src="patches/thy_output.ML"
     dst="$ISABELLE_HOME/src/Pure/Thy/thy_output.ML"
-    if [[ $(md5sum "$src" | cut -d' ' -f1) = $(md5sum "$dst" | cut -d' ' -f1) ]]; then
+     
+    if command -v md5sum > /dev/null 2>&1 && [[ $(md5sum "$src" | cut -d' ' -f1) = $(md5sum "$dst" | cut -d' ' -f1) ]]; then
         echo "  Success: latest Isabelle/DOF patch already applied"
         if isabelle process -e 'Thy_Output.set_meta_args_parser' &> /dev/null ; then
             true
         else
-            echo "  Success: Warning: Isabelle/HOL needs to be rebuild to activate patch."
+            echo "  Warning: Isabelle/HOL needs to be rebuild to activate patch."
         fi
     else
+        command -v md5sum >/dev/null 2>&1 || echo "  Warning: md5sum not available, cannot check if patch is already applied."
         echo "  Warning: Isabelle/DOF patch is not available or outdated."
         echo "           Trying to patch system ...."
 	if (cp $dst $dst.backup-by-isadof-installer && cp -f $src $dst) &> /dev/null; then