Genie:  Clean up FS/property.hh
Genie:  Use int for size constants, not size_t
Genie:  Treat negative property sizes like zero

In other words, a non-positive fixed_size indicates the size isn't fixed
as such.
Genie:  Use -1, not 0 for indeterminate sizes
Genie:  Treat fixed_size = 0 as literal fixed size
Merge branch 'int-property-size'
Genie:   Don't repeat fd get logic in select()

Call relix::get_fd_handle() instead of duplicating its logic.  This will
run more instructions, since the fd_map fetch is done each time, but the
whole point of select() is to wait for something, so this shouldn't have
a negative effect on performance.  Also, it produces smaller object code
and reduces coupling.
Genie:  Pass plain reference to MakeWindow()