Be more specific about the no fullstack on ficus check

util/install/install_stack.sh

@@ -108,10 +108,6 @@ if [[ ! $1 ]]; then
     exit 1
 fi
 stack=$1
-if [[ $stack == "fullstack" ]]; then
-    echo -e "${ERROR}Fullstack is not yet supported for Ficus. Soon..."
-    exit 1
-fi
 shift
 
 # RELEASE is an optional positional argument, defaulting to OPENEDX_RELEASE.
@@ -127,6 +123,11 @@ if [[ ! $release ]]; then
     exit 1
 fi
 
+if [[ $release == *ficus* && $stack == "fullstack" ]]; then
+    echo -e "${ERROR}Fullstack is not yet supported for Ficus. Soon..."
+    exit 1
+fi
+
 # If there are positional arguments left, something is wrong.
 if [[ $1 ]]; then
     echo "Don't understand extra arguments: $*"