[WIP] enable debug_refcell

Author: petrochenkov

library/core/Cargo.toml

@@ -16,6 +16,7 @@ test = false
 bench = false
 
 [features]
+default = ["debug_refcell"]
 # Make panics and failed asserts immediately abort without formatting any message
 panic_immediate_abort = []
 # Choose algorithms that are optimized for binary size instead of runtime performance