Saving a document frees resources and makes it invalid for further editing

[joergbrech]

saveDocument frees resources and sets the document status to SAVED.

tixi/src/tixiInternal.c

Lines 1233 to 1237 in 470570d

	free(document->xmlFilename);
	document->xmlFilename = (char*) malloc(sizeof(char) * (strlen(xmlFilename) + 1));
	strcpy(document->xmlFilename, xmlFilename);
	document->status = SAVED;

As a consequence, a saved document cannot be edited anymore:

tixi/src/tixiImpl.c

Lines 1231 to 1234 in 470570d

	if (document->status == SAVED) {
	printMsg(MESSAGETYPE_ERROR, "Error: Can not add element to document. Document already saved.\n");
	return ALREADY_SAVED;
	}

This is counter-intuitive, because there is also tixiCloseDocument and having intermediate saves in a long simulation run is a valid use case.

Thanks @CLiersch for pointing this out.