Starting /bin/sh in output configure file

[Mohammad Akhlaghi]

Dear Autoconf developers,

I was recently trying to install some packages on a terminal emulator of 
non-rooted Android phone. The terminal emulator has installed all the 
Unix system programs in a separate directory and included that directory 
in all its search paths.

As a result, the command `/bin/sh' is not recognized when you run it on 
the terminal, but the command `sh' is.

Because of this, when you run `./configure' on the terminal emulator it 
complains with an error that it can't run `bin/sh' or later, can't build 
programs.

I was able to solve the second problem by defining `CONFIG_SHELL' which 
will replace `/bin/sh' everywhere in the output `configure' script. 
However, running `./configure' would still complain about not being able 
to run `bin/sh'.

This was very strange for me, because I had set `CONFIG_SHELL'.

After a look, I noticed that the first line of the output `configure' 
script is:

#! /bin/sh

The error was caused by this line. When I manually removed it from 
`configure', the configure script ran successfully and I was able to 
build, check install programs.

It would be great if this first line of the configure script would also 
check for `CONFIG_SHELL' (if its possible), instead of directly calling 
`/bin/sh'.

Thank you very much for all the wonderful work on GNU Autoconf.

Cheers,
Mohammad