Allocate joining players in topmost available slot.
newnet: Remove very-out-of-date newnet.TODO, since newnet is done.
cpp: Remove old fixcppbuild script.

Redundant since ea4e99a92dc76a1fded791328d9584f9385c358c, as everything that should be compiled as C++ already is.
Merge branch 'bugfixes' into 3.1