url: fix UnicodeDecodeError on certificate verification error
SSLSocket.getpeercert() returns tuple containing unicode for 'subject'.
Since Mercurial does't support IDN at all, it just returns error for non-ascii
certname.
$ hg init outer
$ cd outer
hg debugsub with no remapping
$ echo 'sub = http://example.net/libfoo' > .hgsub
$ hg add .hgsub
$ hg debugsub
path sub
source http://example.net/libfoo
revision
hg debugsub with remapping
$ echo '[subpaths]' > .hg/hgrc
$ printf 'http://example.net/lib(.*) = C:\\libs\\\\1-lib\\\n' >> .hg/hgrc
$ hg debugsub
path sub
source C:\libs\foo-lib\
revision
test bad subpaths pattern
$ cat > .hg/hgrc <<EOF
> [subpaths]
> .* = \1
> EOF
$ hg debugsub
abort: bad subrepository pattern in $TESTTMP/outer/.hg/hgrc:2: invalid group reference
[255]