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
running: init test1
result: 0
running: add foo
result: 0
running: commit -m commit1 -d 2000-01-01 foo
result: 0
running: commit -m commit2 -d 2000-01-02 foo
result: 0
running: log -r 0
changeset: 0:0e4634943879
user: test
date: Sat Jan 01 00:00:00 2000 +0000
summary: commit1
result: 0
running: log -r tip
changeset: 1:45589e459b2e
tag: tip
user: test
date: Sun Jan 02 00:00:00 2000 +0000
summary: commit2
result: 0