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').

[originally from svn r6068]