Add a `full' parameter to validate_params(), analogous to the one in

Add a `full' parameter to validate_params(), analogous to the one in
encode_params(). This is necessary for cases where generation-time parameters
that are normally omitted from descriptive IDs can place restrictions on other
parameters; in particular, when the default value of a relevant generation-time
parameter is not the one used to generate the descriptive ID, validation could
reject self-generated IDs (e.g., Net `5x2w:56182ae7c2', and some cases in
`Pegs').

git-svn-id: svn://svn.tartarus.org/sgt/puzzles@6068 cda61777-01e9-0310-a592-d414129be87e