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().

test-ssh: show that stdio redirection doesn't work with chg Running tests with --chg doesn't mean all hg invocations are replaced by chg. This patch explicitly adds the test for "chg serve --stdio", which does weird stdio dance.

revset: make heads(commonancestors(x + x^)) be x^, not x Differential Revision: https://phab.mercurial-scm.org/D4742