rename libc to libjehanne; improve libposix

This is to avoid conflicts between standards' assumptions and Jehanne's choices

sys/src/lib/jehanne/port/getuser.c

@@ -0,0 +1,29 @@
+/*
+ * This file is part of the UCB release of Plan 9. It is subject to the license
+ * terms in the LICENSE file found in the top-level directory of this
+ * distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
+ * part of the UCB release of Plan 9, including this file, may be copied,
+ * modified, propagated, or distributed except according to the terms contained
+ * in the LICENSE file.
+ */
+
+#include <u.h>
+#include <libc.h>
+
+char *
+jehanne_getuser(void)
+{
+	static char user[64];
+	int fd;
+	int n;
+
+	fd = sys_open("/dev/user", OREAD);
+	if(fd < 0)
+		return "none";
+	n = jehanne_read(fd, user, (sizeof user)-1);
+	sys_close(fd);
+	if(n <= 0)
+		return "none";
+	user[n] = '\0';
+	return user;
+}