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
hg init repo
cd repo
cat > a <<EOF
c
c
a
a
b
a
a
c
c
EOF
hg ci -Am adda
cat > a <<EOF
c
c
a
a
dd
a
a
c
c
EOF
echo '% default context'
hg diff --nodates
echo '% invalid --unified'
hg diff --nodates -U foo
echo '% --unified=2'
hg diff --nodates -U 2
echo '% diff.unified=2'
hg --config diff.unified=2 diff --nodates
echo '% diff.unified=2 --unified=1'
hg diff --nodates -U 1
echo '% invalid diff.unified'
hg --config diff.unified=foo diff --nodates
echo % test off-by-one error with diff -p
hg init diffp
cd diffp
echo a > a
hg ci -Ama
rm a
echo b > a
echo a >> a
echo c >> a
hg diff -U0 -p --nodates
exit 0