bug#17330: files.el cd-absolute overcome false negative from file-executable-p

[Philip Hodges <philip.hodges@bluewin.ch>]

> I prefer to solve the problem rather than ask users work around it.

So when can we reasonably expect a guarantee of no more false negatives 
for users of 24.3 without having to inspect the fileio.c and files.el 
and reinvent an undocumented workaround?

It will be great if you really can *solve* the problem, even just for 
this one particular scenario. I already suggested a pathological 
counterexample. Other sources mentioned do indicate that it is 
impossible to solve it reliably in general. But perhaps it will be 
enough in practice.

Only the positive outcome of file-executable-p is documented as "this 
means you can access files in that directory". The negative outcome is 
not explicitly documented as meaning you cannot, yet that is how callers 
are interpreting it. So there is clearly scope for rewriting the 
documentation and changing the callers' logic to match.

Asking the user whether the directory is supposed to be searchable after 
all is not just a workaround. It may well be the only right thing to do. 
In this case he was the person whose umask set the file modes on the 
host system, and he can also inspect them on that system.

fgetacl showed no acl. I will try icacls but it may well be the same.

[I did take a look at fileio.c in trunk with a view to trying to build 
it native and in cygwin for windows. Instead of simply downloading a 
snapshot I ended up reading rather too much of a very long thread about 
whether bzr should be replaced with git, and wondering whether they 
aren't already coexisting as mirrors anyway. So right now I don't have 
much progress to report on trying out candidate preferred solutions.]