forbid username with '\n' at the changelog level
It was already forbidden for ui.username() but no verification were
made for username passed through the commandline.
#!/bin/sh
#
hg init foo
cd foo
touch a
unset HGUSER
echo "[ui]" >> .hg/hgrc
echo "username= foo" >> .hg/hgrc
echo " bar1" >> .hg/hgrc
hg ci -Am m
rm .hg/hgrc
HGUSER=`(echo foo; echo bar2)` hg ci -Am m
hg ci -Am m -u "`(echo foo; echo bar3)`"
true