Always include setup.h as the first header file.

Added a more verbose comment about what strerror_r() can set errno to in
case of failure.
This file still doesn't build on Solaris due to a missing 'sys_nerr' symbol.

lib/curl_strerror.c

@@ -20,8 +20,9 @@
  *
  ***************************************************************************/
 
-#include <curl/curl.h>
 #include "setup.h"
+
+#include <curl/curl.h>
 #include <stdlib.h>
 #include <string.h>
 #include <errno.h>
@@ -503,7 +504,10 @@ const char *Curl_strerror(struct connectdata *conn, int err)
   if (err >= 0 && err < sys_nerr) {
     /* These should be atomic and hopefully thread-safe */
 #ifdef HAVE_STRERROR_R
-    strerror_r(err, buf, max); /* this may set ERANGE! */
+    strerror_r(err, buf, max); 
+    /* this may set errno to ERANGE if insufficient storage was supplied via
+       strerrbuf and buflen to contain the generated message string, or EINVAL
+       if the value of errnum is not a valid error number.*/
 #else
     strncpy(buf, strerror(err), max);
 #endif