Correct documentation for -r,--remote flags and bup on

-r,--remote both correctly user user@host:path notation, but this was
not reflected in the documentation.

bup on allows for user@host:port notation, but this was not reflected in
the documentation.

This patch adds explicit documentation of these features.

Signed-off-by: Will Rouesnel <w.rouesnel@gmail.com>
Fix compression test (t/test.sh:488) rounding errors

The compression test in test.sh can fail due to rounding errors in the
block size used leading to equal apparent sizes for compression 0 and
compression 9 values. There's no reason to use multiples of 1024 bytes
for this test.

Signed-off-by: Will Rouesnel <w.rouesnel@gmail.com>
Add -e,--sshcmd support to remote commands.

Added support for the rsync-style -e command line option to explicitly
specify the command line bup should use for the remote shell. This
allows the use of advanced SSH options by specifying them on the command
line ala:

	bup init -r user@remotehost -e 'ssh -oCompression=yes'
	
or the use of alternate shells which accept addressing and command
invocation in the SSH style.
Revised documentation for the -e,--sshcmd arguments.

Updates the documentation for init, join, save and split to be inline
with the -e,--sshcmd argument and their usage in relation to
-r,--remote.