The existing 'last' clip isn't forwarded after an assignment at the end of a script/scope

[tophf]

The following script

blankclip(1000,720,480,"yv12",color_yuv=$808080)
anotherfilter = blankclip(1000,720,480,"yv12",color_yuv=$FF8080)
# commented_filter()

is erroneously treated as though it doesn't have any video at all because the assignment operator doesn't forward the previous 'last' clip variable to the host application, which is invoking the script (avspmod/virtualdub/encoder/etc).
Yet actually the 'last' clip still exists, if you add "last" to the line below the assignment, it will work.

[pylorak]

Discussion starting at http://forum.doom9.org/showthread.php?p=1651636#post1651636.
Won't fix for concerns summarized in http://forum.doom9.org/showthread.php?p=1651732#post1651732.