chgserver: update comment describing when to fall back to core _runsystem()
The condition "output needs to be captured" was moved to the core ui, and
removed at fbce78c58f1e "chg: refactor ui.system() to be partly overridden."
The next patch will add one more "if" to address the issue 5992.
procutil: compare fd number to see if stdio protection is needed (issue5992)
When I wrote this function for commandserver at 69f86b937035, testing object
identity was suffice, and I was sloppy enough not to compare fileno() values.
However, it doesn't work in chg session because chgserver reopens stdio to
apply new buffering mode.
This patch partially fixes the issue 5992. Still we have another problem in
chgui._runsystem().