load a key that is already loaded. This makes command lines such as
`pageant mykey -c mycommand' almost infinitely more useful.
[originally from svn r1522]
malicious SCP server could have written to areas other than the ones
the user requested; cleared up buffer overruns everywhere. Hopefully
we now do not use arbitrary buffer limits _anywhere_.
[originally from svn r1205]
by ceasing to listen on input channels if the corresponding output
channel isn't accepting data. Has had basic check-I-didn't-actually-
break-anything-too-badly testing, but hasn't been genuinely tested
in stress conditions (because concocting stress conditions is non-
trivial).
[originally from svn r1198]
