* Systems/fuel.xml (JSBSim only): fix that the main tanks would continue to feed
the collector tanks even when empty, leading to infinite range.
* Nasal/systems.nas: replace settimer loops with fixed-frequency maketimer loops.
* b190common.xml: add support for limits; add weight and speed limits.
Also factorize the loading of nasal modules.
* b1900d-set.xml, b1900d-ysm-set.xml: loading of nasal modules factorized above.
