vfs:  Rename geteof and seteof methods

These conflict with similar operations on filehandles, and 'end of file'
is a term rightfully claimed by filehandle I/O, not data storage.
vfs:  Add bstore_method_set (byte store, i.e. REG)

We invent the term 'byte store' to mean a filehandle backed by a regular
file.
vfs:  Add bytestore methods to filehandle set
vfs:  Add filehandle::bstore_methods()
Genie:  Set MemoryFileHandle's filehandle methods
Genie:  Set MacFileHandle's filehandle methods
Genie:  Set PropertyReaderFileHandle's fh methods
Genie:  Set Mac Handle filehandle methods
Genie:  Set TextEdit text filehandle methods
Genie:  Set IconDataFileHandle filehandle methods
Genie:  Set gworld pixels filehandle methods
Genie:  Set bitmap bits filehandle methods
Genie:  Set caption text filehandle methods
vfs:  Add bytestore primitives
Genie:  Call vfs bytestore primitives
Genie:  Axe virtual {p{read,write},{g,s}eteof}()
Merge branch 'bstore'