Returns 1 if file name is executable by the current user, 0 otherwise.
MHo 2010-11-11: Seems not work as expected on MS Windows. file executable gives 0 for a program which is definitely callable. The program resides on a mapped network drive (maybe this is important).
AMG: It works for me, on Windows XP. [file executable] returns 1 for *.exe files and directories, probably others too. It returns 0 for *.dll and *.tcl, I noticed. I'm using a very recent Tcl 8.6 CVS I built myself using MinGW.