Scripts generating automated build failure reports updated

[Andreas Gustafsson <gson%gson.org@localhost>]

I have now updated the scripts that generate the automated build
failure email reports to provide a couple more lines of trailing
context in the extract from the build log, along with some other
tweaks to the algorithm for deciding which part of the build log to
include.

Also, when choosing the version to check out for testing, the scripts
no longer use the time of the newest commit present in the rsynced
repository, but one at least five minutes older than the start of the
rsync.  This should hopefully eliminate a significant source of false
alarms.
-- 
Andreas Gustafsson, gson%gson.org@localhost