test case work
test case support fns, remove debugging test case
new test that uncovers bug in fold
fixed bug in fold's traversal of cast exprs
added test for ptr_eq on fresh_name-generated idents
added gensym_copy mechanism to ensure sharing of pointers in the interner

this makes comparisons constant-time, and enables spelling-comparison
of identifiers, crucial in many parts of resolve.
added IterBytes for 4-tuples
marking on both input and output from macros. nice shiny new test case framework
fix to adding iterbytes for 4-tuples (merge with other commit)
add test case for macro token comparison
add test case for iterbytes on 4-tuples
make comparison of special_idents non-hygienic
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add temporarily unused ctxt field to mac_invoc_tt
WIP
WIP: adding context to macros
add fold_mac field to fold.rs
add fold_mac clause to fun_to_ctxt_folder
capturing macros now implemented
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