top: extend scaled summary memory range to include EiB

This commit increases the upper limit for summary area
memory scaling to 9999.999 Exbibytes. It also enhances
the man page through a helpful table for equivalences.

(now that we know a '.' + 2 spaces is squeezed to one)
(everything's perfectly justified, but it's just luck)

Reference(s):
http://www.freelists.org/post/procps/top-regression-reports
http://www.freelists.org/post/procps/top-enhancements-i-hope,1

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

top/top.h

@@ -194,7 +194,7 @@ enum pflag {
 
         /* The scaling 'target' used with memory fields */
 enum scale_enum {
-   SK_Kb, SK_Mb, SK_Gb, SK_Tb, SK_SENTINEL
+   SK_Kb, SK_Mb, SK_Gb, SK_Tb, SK_Pb, SK_Eb, SK_SENTINEL
 };
 
         /* This typedef just ensures consistent 'process flags' handling */