files with gc_global() instead. Deleted all references to
io_backend in the rest of the source files. Doesn't quite work yet.

Rev: src/client.c:1.130
Rev: src/client.h:1.45
Rev: src/client_x11.c:1.12
Rev: src/gc.h:1.9
Rev: src/interact.h:1.9
Rev: src/io.c:1.148
Rev: src/io.h:1.80
Rev: src/io_commands.c:1.45
Rev: src/io_commands.h:1.20
Rev: src/lsh-decode-key.c:1.10
Rev: src/lsh-export-key.c:1.10
Rev: src/lsh-writekey.c:1.16
Rev: src/lsh.c:1.147
Rev: src/lsh.h:1.22
Rev: src/lsh_proxy.c:1.24
Rev: src/lshd.c:1.124
Rev: src/lshg.c:1.14
Rev: src/reaper.c:1.21
Rev: src/reaper.h:1.10
Rev: src/resource.h:1.12
Rev: src/server_session.c:1.68
Rev: src/server_session.h:1.16
Rev: src/server_userauth.h:1.19
Rev: src/sexp-conv.c:1.9
Rev: src/srp-gen.c:1.11
Rev: src/tcpforward_commands.c:1.36
Rev: src/tcpforward_commands.h:1.6
Rev: src/unix_interact.c:1.12
Rev: src/unix_user.c:1.41