OCaml version problems on Windows

Turns out there are still some lingering issues with the OCaml version of
0install on Windows:

0install sporadically fails with messages like:
Fatal error: exception Unix.Unix_error(Unix.EACCES, "unlink",
"...\\Temp\\0install985d8b-gpg")
This seems to be triggered by some race condition since executing the same
command multiple times in a row sometimes triggers the issue and sometimes
does not. Perhaps it has something to do with a file handle not being
released on time, since Windows gets considerably more grumpy about deleting
"in use" files than Linux does.

Fetching information from the key server fails due to an SSL certificate
problem:
Error downloading
'https://keylookup.appspot.com/key/66B436AC2D4B2281257B9BB985A0F0DAB46EE668'
: SSL certificate problem: unable to get local issuer certificate
I guess this has something to do with OCaml Curl library not being bundled
with a cert list.

I saw a couple of messages like this for feeds are actually correctly
signed:
Feed http://0install.de/feeds/cli/cli.xml: No signatures found on feed
http://0install.de/feeds/cli/cli.xml!
Perhaps a secondary side-effect of one of the two issues above?


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