Submitted as-is as I haven't had a chance to check
how _PLAN9_SOURCES is used yet.  I think this one may need
additional work, but I can't be sure

Notes:
Fri Apr 28 11:50:49 EDT 2006 rsc
    This is not correct.  <unistd.h> is POSIX, so checking _POSIX_SOURCE is correct.
	Also, please run "mk all" in /sys/src/ape to check these changes before
	submitting them.  That should catch most problems with the build.
	
	Thanks.
	Russ
    


Reference: /n/sources/patch/sorry/unistd_h
Date: Fri Apr 28 06:52:13 CES 2006
Signed-off-by: lucio@proxima.alt.za
Reviewed-by: rsc

--- /sys/include/ape/unistd.h	Fri Apr 28 06:51:29 2006
+++ /sys/include/ape/unistd.h	Fri Apr 28 06:51:15 2006
@@ -1,8 +1,9 @@
+#ifndef _RESEARCH_SOURCE
+   This header file is an extension to ANSI/POSIX
+#endif
+
 #ifndef	__UNISTD_H
 #define	__UNISTD_H
-#ifndef _POSIX_SOURCE
-   This header file is not defined in pure ANSI
-#endif
 #pragma lib "/$M/lib/ape/libap.a"
 
 #define _POSIX_VERSION	199309L