[RFC] git send-email hashbang

[Samuel Maftoul <samuel.maftoul@gmail.com>]

I recently contributed for the first time patches on this maillist and
used for the first time `git format-patch` and `git send-email`.
I had hard times making `git send-email` work on my mac, because the
OSX bundled perl was missing the Net::SMTP::SSL module.
So I did `cpan -f Net::SMTP::SSL` (I'm using gmail with smtps/ssl)
which asked me some questions (to setup cpan, I'm not really using
perl usually), and installed the module.
Still `git send-email` wasn't able to find the module.
Actually, during the setup of cpan, I have been asked this:

--------------------------
Warning: You do not have write permission for Perl library directories.

To install modules, you need to configure a local Perl library directory or
escalate your privileges.  CPAN can help you by bootstrapping the local::lib
module or by configuring itself to use 'sudo' (if available).  You may also
resolve this problem manually if you need to customize your setup.

What approach do you want?  (Choose 'local::lib', 'sudo' or 'manual')
--------------------------

I have naturally choosed the default ('local::lib'), but it still didn't worked.

So I choose to not use the system bundled perl and installed my own
perl with homebrew, installed the Net::SMTP::SSL module ... but still
, it didn't worked.
I looked at the send-email script, changed the hashbang to use
/usr/local/bin/perl instead of /usr/bin/perl and it worked !

Then I wondered what happened, and I discovered that using the bundled
cpan's "sudo" approach works, but I'm not very satisfied that I need
to be root to make this script work.
I also found several stackoverflow questions, gists and other
discussiond with people having this exact problem (on osx) with some
different solution (mostly not working, using `sudo cpan` or
whatever).

It seems strange to me that the script doesn't uses "the perl I use in
my environment", that is, I would have thought the `git-send-email.pl`
script had `#!/usr/bin/env perl` as hashbang.
Then, I read that some environment (namely busybox) don't bundle
`/usr/bin/env`, so I understood this might not be portable.
I think there is a solution involving using a combination of /bin/sh
as hashbang and there executing perl with probably the `-x` flag (see
`perldoc perlrun`).
Is it worth proposing a solution for this problem ?

Thanks !