doc: Fix typos

From: Alexander Law <exclusion@gmail.com>

doc/src/sgml/btree-gist.sgml

@@ -98,7 +98,7 @@ INSERT 0 1
   <title>Authors</title>
 
   <para>
-   Teodor Sigaev (<email>teodor@stack.net</email>) ,
+   Teodor Sigaev (<email>teodor@stack.net</email>),
    Oleg Bartunov (<email>oleg@sai.msu.su</email>), and
    Janko Richter (<email>jankorichter@yahoo.de</email>).  See
    <ulink url="http://www.sai.msu.su/~megera/postgres/gist/"></ulink>

doc/src/sgml/ref/pg_xlogdump.sgml

@@ -16,7 +16,7 @@ PostgreSQL documentation
 
  <refnamediv>
   <refname>pg_xlogdump</refname>
-  <refpurpose>Display a human-readable rendering of the write-ahead log of a <productname>PostgreSQL</productname> database cluster</refpurpose>
+  <refpurpose>display a human-readable rendering of the write-ahead log of a <productname>PostgreSQL</productname> database cluster</refpurpose>
  </refnamediv>
 
  <refsynopsisdiv>

doc/src/sgml/sepgsql.sgml

@@ -675,13 +675,13 @@ ERROR:  SELinux: security policy violation
      </row>
      <row>
       <entry><literal>sepgsql_mcstrans_in(text) returns text</literal></entry>
-      <entry>Translates the given qualifies MLS/MCS range into raw format if
+      <entry>Translates the given qualified MLS/MCS range into raw format if
       the mcstrans daemon is running.
       </entry>
      </row>
      <row>
       <entry><literal>sepgsql_mcstrans_out(text) returns text</literal></entry>
-      <entry>Translates the given raw MCS/MCS range into qualified format if
+      <entry>Translates the given raw MLS/MCS range into qualified format if
       the mcstrans daemon is running.
       </entry>
      </row>