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

[Philip Hodges]

> The new f-a-d-p completely ignores permissions

Sorry, I wasn't completely clear. I did not mean that it overcomes permissions 
to give information about the existence of directories that it cannot even see.

Depending on platform the code looks like it checks for a directory (using 
faccessat or stat) or checks existence of the . directory within it. It appears 
to be making checks that depend on certain permissions (in other words actually 
trying it) instead of inspecting permissions (and being misled by them).