[PATCH] pm_trace is dangerous

CONFIG_PM_TRACES scrogs your RTC.  Mark it as experimental, and defaulting to
`off'.

Also beef up the help message a bit.
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

kernel/power/Kconfig

@@ -38,13 +38,22 @@ config PM_DEBUG
 
 config PM_TRACE
 	bool "Suspend/resume event tracing"
-	depends on PM && PM_DEBUG && X86_32
-	default y
+	depends on PM && PM_DEBUG && X86_32 && EXPERIMENTAL
+	default n
 	---help---
 	This enables some cheesy code to save the last PM event point in the
 	RTC across reboots, so that you can debug a machine that just hangs
 	during suspend (or more commonly, during resume).
 
+	To use this debugging feature you should attempt to suspend the machine,
+	then reboot it, then run
+
+		dmesg -s 1000000 | grep 'hash matches'
+
+	CAUTION: this option will cause your machine's real-time clock to be
+	set to an invalid time after a resume.
+
+
 config SOFTWARE_SUSPEND
 	bool "Software Suspend"
 	depends on PM && SWAP && (X86 && (!SMP || SUSPEND_SMP)) || ((FRV || PPC32) && !SMP)