plagiarize could avoid showing unit upgrade options illegal due to faction tech

[high gale]

Our sardakk player asked us if he could plagiarize DN2 and we said no and then the bot listed it as an option. Not sure it's worth implementing but i thought I'd mention it

[cobalt nebula]

I'd classify this as a bug, since we already have some work on this for a normal tech research, just forgot to apply it to plagiarism

Will just throw it on there later today

[high gale]

I dithered