py3: fix broken man page generation, it was generating `(default: NUL*)`
`bytes(default)` was producing things like `(default: \x00)` when handed
non-bytes values such as `1`, `10`, or `True`. The man page generation would
apparently ignore these bytes and produce man pages that had the string
`(default: )`.
Test Plan:
- Ran `cd doc; python3 gendoc.py "hg.1.gendoc"` and grepped for bad output
- Ran `make deb`, extracted the deb, manually inspected `hg.1` file.
Differential Revision: https://phab.mercurial-scm.org/D8639
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present