Genie:  Move new_generated() into namespace vfs
Genie -> vfs:  Move/rename generated_file
Genie:  Use consistent 64K cut-off for temp mem

This changes two things:  A mapping of exactly 64 kilobytes to a regular
file will be backed by malloc() instead of TempNewHandle().  The cut-off
for anonymous memory maps using the application heap is quasi-halved, so
that anything within 64KB and 128KB exclusive is now backed by temporary
memory instead.
Genie -> vfs:  Move malloc_memory_mapping
vfs, MacVFS:  Add map_temporary()
vfs:  Add map_uninitialized()

Use temporary memory for requests larger than 64K (or if malloc() fails)
on Mac OS.  Otherwise, just use malloc().

The map_temporary() function is defined in MacVFS.  Since MacVFS isn't a
prerequisite of vfs (and it can't be, because it's a dependant), linking
to it is non-portable -- i.e. it won't work with a Unix toolchain -- but
it's only required for classic Mac OS anyway, and Metrowerks handles it.
MacVFS:  Rewrite map_anonymous()

Requests of 64K or less will now use malloc() instead of Mac OS handles.
This is likely to improve performance of a hypothetical sequence of many
small requests, should such a pattern occur.
MacVFS -> vfs:  Move map_anonymous()
Genie:  Rewrite RegularFileHandle::Map()

This behavioral no-op hides the details of map_uninitialized().
Merge branches 'map_anonymous' and 'file-mmap'