that span two reads.

so that the client will be able to cooperate with keep-alive.

Files-from data is now sent as multiplexed I/O so that it can mingle
with any messages (such as debug output).  Requires protocol 31.

Protocol 31 no longer disables output verbosity in a couple instances
that used to cause protocol issues.

Got rid of MSG_* messages that have implied raw data that follows after
them.  We instead send a negative index value as a part of the raw data
stream, which is guaranteed to be output together with the following
data.  This only affects the (in-progress) protocol 31 and the (self-
contained) communication stream from the receiver to the generator.

Added --debug=IO and improved --debug=FLIST.  Some --debug=IO output
requires --msgs2stderr to be used to see it (i.e. sending a message
about sending a message would send another message, ad infinitum).

by using inline functions for the 4-char <-> uint32 conversions.

Use simpler multiplexed-out stopping method.
Make sure we can't false-match a socket fd.

for the data that goes from the receiver to the generator.

file that hasn't really been created.

NO_SYMLINK_XATTRS is defined.

If a symlink, device, special-file, or hard-linked file is replacing
an existing non-directory, the new file is created using a temporary
filename and then renamed into place.  Also changed the handling of
a cluster of hard-linked symlinks/devices/special-files to always
ensure the first item in the cluster is correct, since it doesn't
really save any significant work to try to find an existing correct
item later in the cluster to link with.

Fixes bug 6569.