WordPlain.c parseDocumentRels requires C99

Allowance of declarations intermixed in statements is a C99 feature. It is a nice feature.

I notice that WordPlain.c function parseDocumentRels() depends on it.

Are we depending on that for all compilers that are used?

Are we compiling as Standard C? (i.e., no extensions)?

(This is probably not a JIRA issue, but it seems like a good idea to have it captured in an easy-to-find place.