Changeset 0c50ce3 in git

src/extend.c,src/img.c,src/img.h: Repurpose the long unused fBinary
parameter to img_open_write() as a flags parameter, and add
img_FFLAG_EXTENDED to specify that this is an extended elevation,
in place of appending " (extended)" to the title. Internally we
still append this to the title (and remove it upon reading), but in
the 3d v8 format, the flags will be stored explicitly in the file.