Parse a constant, which might be qualified by one or more class or module
names
# File lib/rdoc/parser/ruby.rb, line 310
def get_constant
res = ""
skip_tkspace false
tk = get_tk
while TkCOLON2 === tk or TkCOLON3 === tk or TkCONSTANT === tk do
res += tk.name
tk = get_tk
end
# if res.empty?
# warn("Unexpected token #{tk} in constant")
# end
unget_tk(tk)
res
end