Re: [PATCH v2] help: improve is_executable() on Windows

Johannes Schindelin [off-list ref] writes:

From: Heiko Voigt <redacted>

On Windows, executables need to have the file extension `.exe`, or they
are not executables. Hence, to support scripts, Git for Windows also
looks for a she-bang line by opening the file in question, and executing
it via the specified script interpreter.

To figure out whether files in the `PATH` are executable, `git help` has
code that imitates this behavior. With one exception: it *always* opens
the files and looks for a she-bang line *or* an `MZ` tell-tale
(nevermind that files with the magic `MZ` but without file extension
`.exe` would still not be executable).

Opening this many files leads to performance problems that are even more
serious when a virus scanner is running. Therefore, let's change the
code to look for the file extension `.exe` early, and avoid opening the
file altogether if we already know that it is executable.

Much more readable than the initial round.  Will queue; thanks.