fix #51: added a check into umount_tomb() before removing mount point: if it's the default one, then delete it

src/tomb

@@ -955,9 +955,12 @@ umount_tomb() {
 	if ! [ $? = 0 ]; then
 	    error "Tomb is busy, cannot umount!"
 	else   
+        # this means we used a "default" mount point
+        if [ "${tombmount}" = "/media/${tombname}.tomb" ]; then
 	        rmdir ${tombmount}
         fi
 	fi
+    fi
 
     cryptsetup luksClose $mapper
     if ! [ $? = 0 ]; then