Fixed namespace pollution in uma changes:

- use `struct uma_zone *' instead of uma_zone_t, so that <sys/uma.h> isn't
  a prerequisite.
- don't include <sys/uma.h>.
Namespace pollution makes "opaque" types like uma_zone_t perfectly
non-opaque.  Such types should never be used (see style(9)).

sys/sys/proc.h

@@ -57,7 +57,6 @@
 #endif
 #include <sys/ucred.h>
 #include <machine/proc.h>		/* Machine-dependent proc substruct. */
-#include <vm/uma.h>
 
 /*
  * One structure allocated per session.
@@ -773,7 +772,7 @@ extern struct proclist zombproc;	/* List of zombie processes. */
 extern struct proc *initproc, *pageproc; /* Process slots for init, pager. */
 extern struct proc *updateproc;		/* Process slot for syncer (sic). */
 
-extern uma_zone_t proc_zone;
+extern struct uma_zone *proc_zone;
 
 extern int lastpid;