gioerror: map some more values to G_IO_ERROR_NOT_SUPPORTED

Map EPROTONOSUPPORT, ESOCKTNOSUPPORT, EPFNOSUPPORT and EAFNOSUPPORT to
G_IO_ERROR_NOT_SUPPORTED in g_io_error_from_errno(). (GSocket's
socket_io_error_from_errno() already did this with the corresponding
Winsock errors.)

Also map EOPNOTSUPP, which on Linux is the same as ENOTSUP, but may
not be on other platforms.

Also, rewrite the EAGAIN/EWOULDBLOCK section to use the simpler idiom
used by EEXIST/ENOTEMPTY and (now) ENOTSUP/EOPNOTSUPP.

gio/gioenums.h

@@ -432,7 +432,7 @@ typedef enum {
  * @G_IO_ERROR_NO_SPACE: No space left on drive.
  * @G_IO_ERROR_INVALID_ARGUMENT: Invalid argument.
  * @G_IO_ERROR_PERMISSION_DENIED: Permission denied.
- * @G_IO_ERROR_NOT_SUPPORTED: Operation not supported for the current backend.
+ * @G_IO_ERROR_NOT_SUPPORTED: Operation (or one of its parameters) not supported
  * @G_IO_ERROR_NOT_MOUNTED: File isn't mounted.
  * @G_IO_ERROR_ALREADY_MOUNTED: File is already mounted.
  * @G_IO_ERROR_CLOSED: File was closed.

gio/gioerror.c

@@ -134,7 +134,8 @@ g_io_error_from_errno (gint err_no)
       break;
 #endif
 
-#if defined(ENOTEMPTY) && (!defined (EEXIST) || (ENOTEMPTY != EEXIST))
+    /* ENOTEMPTY == EEXIST on AIX for backward compatibility reasons */
+#if defined (ENOTEMPTY) && (!defined (EEXIST) || (ENOTEMPTY != EEXIST))
     case ENOTEMPTY:
       return G_IO_ERROR_NOT_EMPTY;
       break;
@@ -146,6 +147,37 @@ g_io_error_from_errno (gint err_no)
       break;
 #endif
 
+    /* EOPNOTSUPP == ENOTSUP on Linux, but POSIX considers them distinct */
+#if defined (EOPNOTSUPP) && (!defined (ENOTSUP) || (EOPNOTSUPP != ENOTSUP))
+    case EOPNOTSUPP:
+      return G_IO_ERROR_NOT_SUPPORTED;
+      break;
+#endif
+
+#ifdef EPROTONOSUPPORT
+    case EPROTONOSUPPORT:
+      return G_IO_ERROR_NOT_SUPPORTED;
+      break;
+#endif
+
+#ifdef ESOCKTNOSUPPORT
+    case ESOCKTNOSUPPORT:
+      return G_IO_ERROR_NOT_SUPPORTED;
+      break;
+#endif
+
+#ifdef EPFNOSUPPORT
+    case EPFNOSUPPORT:
+      return G_IO_ERROR_NOT_SUPPORTED;
+      break;
+#endif
+
+#ifdef EAFNOSUPPORT
+    case EAFNOSUPPORT:
+      return G_IO_ERROR_NOT_SUPPORTED;
+      break;
+#endif
+
 #ifdef ETIMEDOUT
     case ETIMEDOUT:
       return G_IO_ERROR_TIMED_OUT;
@@ -158,30 +190,17 @@ g_io_error_from_errno (gint err_no)
       break;
 #endif
 
-/* some magic to deal with EWOULDBLOCK and EAGAIN.
+#ifdef EWOULDBLOCK
- * apparently on HP-UX these are actually defined to different values,
- * but on Linux, for example, they are the same.
- */
-#if defined(EWOULDBLOCK) && defined(EAGAIN) && EWOULDBLOCK == EAGAIN
-    /* we have both and they are the same: only emit one case. */
-    case EAGAIN:
-      return G_IO_ERROR_WOULD_BLOCK;
-      break;
-#else
-    /* else: consider each of them separately.  this handles both the
-     * case of having only one and the case where they are different values.
-     */
-# ifdef EAGAIN
-    case EAGAIN:
-      return G_IO_ERROR_WOULD_BLOCK;
-      break;
-# endif
-
-# ifdef EWOULDBLOCK
     case EWOULDBLOCK:
       return G_IO_ERROR_WOULD_BLOCK;
       break;
-# endif
+#endif
+
+    /* EWOULDBLOCK == EAGAIN on most systems, but POSIX considers them distinct */
+#if defined (EAGAIN) && (!defined (EWOULDBLOCK) || (EWOULDBLOCK != EAGAIN))
+    case EAGAIN:
+      return G_IO_ERROR_WOULD_BLOCK;
+      break;
 #endif
 
 #ifdef EMFILE