gnuplot-4.4.0-rc1 breaks gnuplot script

[Teo S B. <teo...@gm...>]

Problem:
Gnuplot script that set parameter repeatedly in plot command to address the
data index (within a data file) does not work when using gnuplot version
4.4.0-rc1.
It works in 4.2 version and, from memory, did also work in version 4.3. See
the below shortened example reproducing the error message:


# file: trial.gpl
f(x)=x
plot a=1, \
     f(x)*a   title "data from index a=1" w l lw 2 lt a ,  a=a+1,       \
     f(x)*a   title "data from index a=2" w l lw 2 lt a ,  a=a+1,       \
     a=0

pause -1 "Continue?"

#
# gnuplot 4.2 patchlevel 5 accepts the above. I believe that also
# gnuplot 4.3 accepted this.
#
# gnuplot-4.4.0 patchlevel 0-rc1 give error:
#    "trial.gpl", line 6: function to plot expected
#
#
#  It works if I add a dummy curve after a=0, so that last line
#  becomes:
#                   a=0, x/0
#
exit

Best regards
Teo