Improvements:
* Minor improvements to fluid pipe extraction, fillers and pipe icon handling (asie)

Bugfixes:
* [#2564] BC pipes lose liquid when different fluids mix in them. (asie - thanks MatthiasM2 for the 6.4.x workaround)
* Combustion engine not updating the fuel RF/t value (asie)
* Error while loading robot resources (hea3ven)
* Invalid engine rendering size (asie - introduced in 6.4.6)
