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 a
cd a
echo a > a
hg add -n
hg st
hg add
hg st
hg forget a
hg add
hg st
echo b > b
hg add -n b
hg st
hg add b || echo "failed to add b"
hg st
echo % should fail
hg add b
hg st
hg ci -m 0 --traceback
echo % should fail
hg add a
echo aa > a
hg ci -m 1
hg up 0
echo aaa > a
hg ci -m 2
hg merge
hg st
echo % should fail
hg add a
hg st
hg resolve -m a
hg ci -m merge
echo % issue683
hg forget a
hg add a
hg st
hg rm a
hg st
echo a > a
hg add a
hg st
hg add c && echo "unexpected addition of missing file"
echo c > c
hg add d c && echo "unexpected addition of missing file"
hg st