workingctx: correctly compute the flag for noexec filesystems+merge
This bug happens if the filesystem doesn't support exec-bit, during merges,
for example in 24ed7a541f23 on the hg repo.
If f is not in p1, but is in p2 and has the x-bit in p2, since the dirstate is
based on p1, and the FS doesn't support the exec-bit, the dirstate can't
"guess" the right bit.
We instead fix it in workingcontext.flags()/manifest.
#!/bin/sh
cat >> $HGRCPATH <<EOF
[extensions]
convert=
EOF
# Prepare orig repo
hg init orig
cd orig
echo foo > foo
HGUSER='user name' hg ci -qAm 'foo'
cd ..
# Explicit --authors
cat > authormap.txt <<EOF
user name = Long User Name
# comment
this line is ignored
EOF
hg convert --authors authormap.txt orig new
echo $?
cat new/.hg/authormap
hg -Rnew log
rm -rf new
# Implicit .hg/authormap
hg init new
mv authormap.txt new/.hg/authormap
hg convert orig new
echo $?
hg -Rnew log