Revert "rm sys/types.h include and improve portability"

This reverts commit db1dcafd03.

This is needed. Tested on an (old) Slackware 11 install.

sfeed_atom.c

@@ -1,3 +1,5 @@
+#include <sys/types.h>
+
 #include <stdio.h>
 #include <string.h>
 #include <time.h>

sfeed_curses.c

@@ -4,6 +4,7 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 
+#include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <locale.h>

sfeed_frames.c

@@ -1,3 +1,5 @@
+#include <sys/types.h>
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

sfeed_gopher.c

@@ -1,3 +1,5 @@
+#include <sys/types.h>
+
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>

sfeed_html.c

@@ -1,3 +1,5 @@
+#include <sys/types.h>
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

sfeed_plain.c

@@ -1,3 +1,5 @@
+#include <sys/types.h>
+
 #include <locale.h>
 #include <stdio.h>
 #include <string.h>

sfeed_twtxt.c

@@ -1,3 +1,5 @@
+#include <sys/types.h>
+
 #include <stdio.h>
 #include <string.h>
 #include <time.h>