Make Cantor working with Sage 9.2

BUG: 428961
FIXED-IN: 20.12

src/backends/sage/cantor-execsage

@@ -2,11 +2,21 @@
 
 export SAGE_ROOT="$($1 --root)"
 
+# Sage 9.2 stop source sage-env-config automatically, so do it manually
 if [[ -f $SAGE_ROOT"/bin/sage-env" ]]; then
+    if [[ -f $SAGE_ROOT"/bin/sage-env-config" ]]; then
+        source "$SAGE_ROOT/bin/sage-env-config" >&2
+    fi
     . "$SAGE_ROOT/bin/sage-env" >&2
 elif [[ -f $SAGE_ROOT"/local/bin/sage-env" ]]; then
+    if [[ -f $SAGE_ROOT"/local/bin/sage-env-config" ]]; then
+        source "$SAGE_ROOT/local/bin/sage-env-config" >&2
+    fi
     . "$SAGE_ROOT/local/bin/sage-env" >&2
 elif [[ -f $SAGE_ROOT"/src/bin/sage-env" ]]; then
+    if [[ -f $SAGE_ROOT"/src/bin/sage-env-config" ]]; then
+        source "$SAGE_ROOT/src/bin/sage-env-config" >&2
+    fi
     . "$SAGE_ROOT/src/bin/sage-env" >&2
 fi