unrelated error message if file listed in AC_CONFIG_SRCDIR does not exist

[Felix Lechner]

Perhaps there should be a warning if ${srcdir} is adjusted
automatically.  In my case, I had listed src/constants.h in
AC_CONFIG_SRCDIR but removed it, so that it could be built from other
sources.  A copy of the file also existed outside the package tree in
../src.

Without a warning ${scrdir} defaulted to ".." causing the "ls -Lt"
test to fail.  The resulting error was difficult to identify:

checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... configure: error: ls -t
appears to fail.  Make sure there is not a broken
alias in your environment
configure: error: newly created file is older than distributed files!
Check your system clock

In my case it would have been more appropriate to either print a
warning about the adjustment of ${srcdir} or print the more
comfortable notice:

configure: error: cannot find sources (src/constants.h)

Maybe it would even make sense to test for the presence of "configure"
before looking outside the package tree.  Of course, these are just
suggestions.  My experience with autotools is very limited.

Autoconf 2.64 on Ubuntu 9.10 (karmic) amd64.

Sincerely,
Felix Lechner