fix collect() breakage introduced by 9366bfb
only report original traceback from plugin thread when we have it

and in addition to the parent traceback, not instead of, since both
could be useful.
truncate plugin results if necessary

The results dict can get huge and push urxvt-256-color into an infinite
loop for some reason.
handle github pagination more robustly

Now we parse the Link: header in a manner compliant with RFC5988.
Merge pull request #39 from aspiers/fixes

Various fixes