It is alway good to find a bug :)

At line 16919 of the configure script we have:
        elif test $GPMAJOR -eq 4 && test $GPMINOR -ge 2 ; then
It should be:
        elif test $GPMAJOR -eq 4 && test $GPMINOR -ge 4 ; then

----
This was allowing to build gretl GUI with:
[jboss@candy-house gretl]$ gnuplot --version
gnuplot 4.2 patchlevel 6

The correct error was presented when producing plots.
---

I have automated:
make clean
cvs update
configure
make
make install

Other tests would follow (but still expploring)
(No success in having the results passed to Testlink)

(Using CentOS 6.4 in an i686 machine)

Hélio