Update documentation on may/can/might:

Standard English uses "may", "can", and "might" in different ways:

        may - permission, "You may borrow my rake."

        can - ability, "I can lift that log."

        might - possibility, "It might rain today."

Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice.  Similarly, "It may crash" is better stated, "It might crash".

Also update two error messages mentioned in the documenation to match.

doc/src/sgml/reference.sgml

@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/reference.sgml,v 1.61 2007/01/23 05:07:17 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/reference.sgml,v 1.62 2007/01/31 20:56:18 momjian Exp $ -->
 
 <part id="reference">
  <title>Reference</title>
@@ -9,7 +9,7 @@
    length an authoritative, complete, and formal summary about their
    respective subjects.  More information about the use of
    <productname>PostgreSQL</productname>, in narrative, tutorial, or
-   example form, may be found in other parts of this book.  See the
+   example form, can be found in other parts of this book.  See the
    cross-references listed on each reference page.
   </para>
 
@@ -159,7 +159,7 @@
     This part contains reference information for
     <productname>PostgreSQL</productname> client applications and
     utilities.  Not all of these commands are of general utility, some
-    may require special privileges.  The common feature of these
+    might require special privileges.  The common feature of these
     applications is that they can be run on any host, independent of
     where the database server resides.
    </para>