Re: exec-path "/:" prefix; file-name-handler-*; start-process

[Richard Stallman]

    Why does initializing `exec-path' need to prepend a "/:" to paths that
    "would otherwise be treated as magic" ?

Because without that they really would mean something else.
If you have a directory /foo:, Emacs would get confused by the
name /foo: without the /: in front.

    All single-directory (single slash) paths in PATH such as /bin turn into
    /:/bin.

The name /bin is not really magic, but it seems to be magic
because of the hostname completion facility.
These names don't need to have /: added, and should not have it.

In the current development version, /: is not added to them.
I am not sure what caused the change; perhaps it has to do
with installing Tramp.  It could be that this has introduced
some other bug or that the hostname completion facility
has been deactivated.  Kai, could you see whether the hostname completion
facility still works?

Anyway, I fixed this problem for 21.3.

    On many systems bash is first found in /bin. (which "bash") finds
    "/:/bin/bash" since (file-executable-p "/:/bin/bash") returns t. However,
    "/:/bin/bash" is not acceptable as an `explicit-shell-file-name' for
    `shell' since it eventually calls `comint-exec' which calls
    `start-process'.

"/:/bin/bash" is a valid name in Emacs for that file,
so it should work in start-process.  I fixed that, and
call-process too.