Add %option nodefault to all our flex lexers. Fix a couple of rule gaps

exposed thereby.  AFAICT these would not lead to any worse problems than
junk emitted on the backend's stdout, but we should have the option to
catch possible worse errors in future.

contrib/cube/cubescan.l

@@ -26,6 +26,7 @@ void cube_scanner_finish(void);
 
 %option 8bit
 %option never-interactive
+%option nodefault
 %option nounput
 %option noyywrap
 %option prefix="cube_yy"
@@ -44,7 +45,7 @@ float        ({integer}|{real})([eE]{integer})?
 \(           yylval = "("; return O_PAREN;
 \)           yylval = ")"; return C_PAREN;
 \,           yylval = ")"; return COMMA;
-[ ]+         /* discard spaces */
+[ \t\n\r\f]+ /* discard spaces */
 .            return yytext[0]; /* alert parser of the garbage */
 
 %%