src/Makefile.am: Regenerate gradient.pov is gdtconvert changes.
doc/manual.sgml,lib/survex.pot,src/,tests/Makefile.am,
tests/cavern.tst: Add more anonymous station types - a double
separator ('..' by default) is an anoymous wall point at the end
of an implicit splay (c.f. '.' being a non-wall point), and
a triple separator ('...' by default) is an anoymous point (with
nothing special about the leg).  New *alias command allows '-' to be
mapped to '..' to match pocket topo conventions.  3d file format now
support a 'WALL' station flag.