Set cwd to '/' for the process executing insmod.

Ricardo has pointed out that under Solaris the cwd is set to '/'
during module load, while under Linux it is set to the callers cwd.
To handle this cleanly I've reworked the module *_init()/_exit()
macros so they call a *_setup()/_cleanup() function when any SPL
dependent module is loaded or unloaded.  This gives us a chance to
perform any needed modification of the process, in this case changing
the cwd.  It also handily provides a way to avoid creating wrapper
init()/exit() functions because the Solaris and Linux prototypes
differ slightly.  All dependent modules should now call the spl
helper macros spl_module_{init,exit}() instead of the native linux
versions.

Unfortunately, it appears that under Linux there has been no consistent
API in the kernel to set the cwd in a module.  Because of this I have
had to add more autoconf magic than I'd like.  However, what I have
done is correct and has been tested on RHEL5, SLES11, FC11, and CHAOS
kernels.

In addition, I have change the rootdir type from a 'void *' to the
correct 'vnode_t *' type.  And I've set rootdir to a non-NULL value.

module/splat/splat-ctl.c

@@ -608,7 +608,7 @@ static struct cdev splat_cdev = {
 	.kobj   =	{ .name = SPLAT_NAME, },
 };
 
-static int __init
+static int
 splat_init(void)
 {
 	dev_t dev;
@@ -667,7 +667,7 @@ error:
 	return rc;
 }
 
-static void
+static int
 splat_fini(void)
 {
 	dev_t dev = MKDEV(SPLAT_MAJOR, 0);
@@ -695,10 +695,12 @@ splat_fini(void)
 	ASSERT(list_empty(&splat_module_list));
 	printk(KERN_INFO "SPLAT: Unloaded Solaris Porting LAyer "
 	       "Tests v%s\n", SPL_META_VERSION);
+
+	return 0;
 }
 
-module_init(splat_init);
-module_exit(splat_fini);
+spl_module_init(splat_init);
+spl_module_exit(splat_fini);
 
 MODULE_AUTHOR("Lawrence Livermore National Labs");
 MODULE_DESCRIPTION("Solaris Porting LAyer Tests");