Warn about initdb using mount-points

Add code to detect and warn about trying to initdb or create pg_xlog on
mount points.

src/port/pgcheckdir.c

@@ -31,6 +31,7 @@ pg_check_dir(const char *dir)
 	int			result = 1;
 	DIR		   *chkdir;
 	struct dirent *file;
+	bool		dot_found = false;
 
 	errno = 0;
 
@@ -47,15 +48,26 @@ pg_check_dir(const char *dir)
 			/* skip this and parent directory */
 			continue;
 		}
+#ifndef WIN32
+		/* file starts with "." */
+		else if (file->d_name[0] == '.')
+		{
+			dot_found = true;
+		}
+		else if (strcmp("lost+found", file->d_name) == 0)
+		{
+			result = 3;			/* not empty, mount point */
+			break;
+		}
+#endif
 		else
 		{
-			result = 2;			/* not empty */
+			result = 4;			/* not empty */
 			break;
 		}
 	}
 
 #ifdef WIN32
-
 	/*
 	 * This fix is in mingw cvs (runtime/mingwex/dirent.c rev 1.4), but not in
 	 * released version
@@ -69,5 +81,9 @@ pg_check_dir(const char *dir)
 	if (errno != 0)
 		result = -1;			/* some kind of I/O error? */
 
+	/* We report on dot-files if we _only_ find dot files */
+	if (result == 1 && dot_found)
+		result = 2;
+
 	return result;
 }