Monkey with JarUrlConnection to make it work when LANG unset

The problem all along has been in AsciiBytes, so the fix in
commit ce3aaf was just a stop gap for a system where multi-byte
characters are supported but the default encoding is not UTF-8 (e.g.
most Windows systems). The real solution is not to leave it to
chance and always pick an encoding for the JarEntry names (i.e.
in AsciiBytes).

(Cherry picked from commit 06e364a9ff5b5fce76ba93277ad6eb940f0dc1d3)

Fixes gh-764
Protect against malformed URLs on Windows

Update JarFile to correctly create system independent URLs to prevent
potential URISyntaxExceptions when running on Windows.

Fixes gh-836