build grep-2.5.1a fails if configure in obj dir different from src dir

[anirkko]

Hi
build grep-2.5.1a fails (with misleading message) if configuring
in an empty obj dir different from the src dir (for most other
GNU packages, this is allowed):

mkdir grep-2.5.1a_obj
cd  grep-2.5.1a_obj
../grep-2.5.1a/configure

checking for a BSD-compatible install... /usr/local/bin/ginstall -c
checking whether build environment is sane... yes
checking for gawk... gawk
checking whether make sets ${MAKE}... yes
configure: error: source directory already configured; run "make distclean" 
there first

Greetings,
Arto