squawk if attached to wrong PANDA

panda/Package.pp

@@ -40,6 +40,9 @@
   #if $[eq $[PANDA],]
     #error You seem to be attached to some trees, but not PANDA!
   #endif
+  #if $[ne $[canonical $[PANDA]], $[canonical $[TOPDIR]]]
+    #error You are not attached to the right PANDA!
+  #endif
 #else
   #defer PANDA_INSTALL $[unixfilename $[INSTALL_DIR]]
   #defer PANDA_INSTALL_OTHER $[unixfilename $[INSTALL_DIR]]