Modify 4_save_and_restore_flags and 9_allocate_slots to use PUSHF/POPF when the stack is safe

[pgoodman]

This would be nice as a command-line option tunable that is on by default. This will require an extra boolean flag in the FlagZone structure to communicate to the slot allocator that all slots should be slightly displaced.

[pgoodman]

This relates to #98 in that, if all partitions are merged, i.e. there is only one partition, then this optimization would only be valid iff all fragment stacks are valid.