Take any `configure` script and move it to another directory. For
example, executing the script from Emacs gives
```
configure: error: cannot find sources (src/lisp.h) in . or ..
```
which is ok. However, and I consider this a bug, you get exactly the
same error message if you say `./configure --help`. In other words,
the user has no chance to find out that there exists a `--srcdir`
option to override `AC_CONFIG_SRCDIR`.
I thus suggest to either make `./configure --help` always work, or at
least change the above error message to something like
```
configure: error: cannot find sources (src/lisp.h) in . or ..
Are you missing a `--srcdir=DIR` command line option?
```
It is probably another bug that a line like
```
AC_CONFIG_HEADERS(src/config.h:src/config.in)
```
fails with
```
config.status: error: cannot find input file: `src/config.in'
```
inspite of a `--srcdir` option...
Werner
