More post-release checklist updates, and a new script.

More post-release checklist updates, and a new script.

I've added a few sample shell commands in the upload procedure (mostly
so that I don't have to faff about remembering how rsync trailing
slashes work every time), and also written a script called
'release.pl', which automates the updating of the version number in
all the various places it needs to be done and also ensures the PSCP
and Plink transcripts in the docs will match the release itself.