This prevents recompiling everything when you are changing just a doc, or
touching only one file among hundreds of sources, just because the
`gen_version.h` is changed, especially since only one source actually
depends on that header.
To avoid everything pulling in HTLCs stuff to the opening daemon, we
split the channel and commit_tx routines into initial_channel and
initial_commit_tx (no HTLC support) and move full HTLC supporting versions
into channeld.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>