Add NULL space mention.

doc/FAQ

@@ -1,7 +1,7 @@
 
                 Frequently Asked Questions (FAQ) for PostgreSQL
                                        
-   Last updated: Mon Jun 24 23:35:08 EDT 2002
+   Last updated: Thu Jul 4 15:25:57 EDT 2002
    
    Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
    
@@ -707,6 +707,8 @@
    Indexes do not require as much overhead, but do contain the data that
    is being indexed, so they can be large also.
    
+   NULLs are stored in bitmaps, so they use very little space.
+   
     4.7) How do I find out what tables, indexes, databases, and users are
     defined?
     

doc/src/FAQ/FAQ.html

@@ -14,7 +14,7 @@
   alink="#0000ff">
     <H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
 
-    <P>Last updated: Mon Jun 24 23:35:08 EDT 2002</P>
+    <P>Last updated: Thu Jul  4 15:25:57 EDT 2002</P>
 
     <P>Current maintainer: Bruce Momjian (<A href=
     "mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
@@ -909,6 +909,9 @@
     <P>Indexes do not require as much overhead, but do contain the data
     that is being indexed, so they can be large also.</P>
 
+    <P><SMALL>NULL</SMALL>s are stored in bitmaps, so they
+    use very little space.</P>
+    
     <H4><A name="4.7">4.7</A>) How do I find out what tables, indexes,
     databases, and users are defined?</H4>