library: rename the 'slab' sources as 'slabinfo' files

Where possible, libprocps files convey the name of the
actual source pseudo file under the '/proc' directory.

This patch brings slab into line with such a standard.

Signed-off-by: Jim Warner <james.warner@comcast.net>

proc/procps.h

@@ -23,7 +23,7 @@
 #include <proc/meminfo.h>
 #include <proc/namespace.h>
 #include <proc/pids.h>
-#include <proc/slab.h>
+#include <proc/slabinfo.h>
 #include <proc/stat.h>
 #include <proc/sysinfo.h>
 #include <proc/version.h>