* Bootstrapping
  * allow reloading library
  * library compiler
    * replace lazy var refs
  * builtin syntax refs
* Builtin sanity:
  * Table: slot, name, min args, max args or -1
* finish bignums
  * Karatsuba
* finish builtins
  * numeric I/O: round-trip float conversion
  * finish sc_div_extended in asm-generic.c
  * rational/complex
* GC symbols and file descriptors
* R5RS hygienic macros, let-syntax
* syntax/variable shadowing
* track open output ports; auto-flush on timer
* deal with SIGPIPE
* more EINTR cases e.g. connect()
* sendto, recvfrom, tests for datagram sockets