Sf crash if no star

Hey, here is the merge request that adds the option of crashing the code if there is not enough space in the extra part buffer.

Just for information, I am currently working on GEAR's star formation that turns into a star only a fraction of a gas particle. Therefore, my error message is already taking into account the creation of new gparts.

I have also included a small fix to configure.ac (the names in the task order option were not consistent [none / default]) and I added the global run time parameter --gear. If you wish, I can do a merge request for each of them.