bupsplit.c: remove extra-large stack-allocated array from selftest().
bupsplit.c: remove extra-large stack-allocated array from selftest().

In some rare cases involving userspace threads (where you're running the
selftest function for some reason?) this could cause stack overflow or
excess memory usage.  Let's just do it with plain malloc().

Signed-off-by: Avery Pennarun <e03ccfb89d416c4697ad6970ce86a92c1c28a78e@gmail.com>

mhoeher/bup,ToxicFrog/bup,jbaber/bup,jbaber/bup,jbaber/bup,ToxicFrog/bup,pombredanne/bup,gevaerts/bup,jbaber/bup,mhoeher/bup,gevaerts/bup,mhoeher/bup,apenwarr/bup,gevaerts/bup,jbaber/bup,tjanez/bup,pombredanne/bup,pombredanne/bup,tjanez/bup,pombredanne/bup,apenwarr/bup,gevaerts/bup,jbaber/bup,ToxicFrog/bup,mhoeher/bup,ToxicFrog/bup,tjanez/bup,gevaerts/bup,ToxicFrog/bup,tjanez/bup,mhoeher/bup,pombredanne/bup,mhoeher/bup,tjanez/bup,apenwarr/bup,pombredanne/bup,apenwarr/bup,tjanez/bup