Make a code-cleanup pass over the collations patch.

This patch is almost entirely cosmetic --- mostly cleaning up a lot of
neglected comments, and fixing code layout problems in places where the
patch made lines too long and then pgindent did weird things with that.
I did find a bug-of-omission in equalTupleDescs().

doc/src/sgml/ref/create_collation.sgml

@@ -108,8 +108,8 @@ CREATE COLLATION <replaceable>name</replaceable> FROM <replaceable>existing_coll
      <listitem>
       <para>
        The name of an existing collation to copy.  The new collation
-       will have the same properties as the existing one, but they
-       will become independent objects.
+       will have the same properties as the existing one, but it
+       will be an independent object.
       </para>
      </listitem>
     </varlistentry>
@@ -134,7 +134,8 @@ CREATE COLLATION <replaceable>name</replaceable> FROM <replaceable>existing_coll
   <title>Examples</title>
 
   <para>
-   To create a collation from the locale <literal>fr_FR.utf8</literal>
+   To create a collation from the operating system locale
+   <literal>fr_FR.utf8</literal>
    (assuming the current database encoding is <literal>UTF8</literal>):
 <programlisting>
 CREATE COLLATION french (LOCALE = 'fr_FR.utf8');

doc/src/sgml/ref/create_domain.sgml

@@ -90,7 +90,7 @@ CREATE DOMAIN <replaceable class="parameter">name</replaceable> [ AS ] <replacea
        <para>
         An optional collation for the domain.  If no collation is
         specified, the underlying data type's default collation is used.
-        The underlying type must be collatable when <literal>COLLATE</>
+        The underlying type must be collatable if <literal>COLLATE</>
         is specified.
        </para>
       </listitem>

doc/src/sgml/ref/create_index.sgml

@@ -188,9 +188,8 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ <replaceable class="parameter">name</
         The name of the collation to use for the index.  By default,
         the index uses the collation declared for the column to be
         indexed or the result collation of the expression to be
-        indexed.  Indexes with nondefault collations are
-        available for use by queries that involve expressions using
-        nondefault collations.
+        indexed.  Indexes with non-default collations can be useful for
+        queries that involve expressions using non-default collations.
        </para>
       </listitem>
      </varlistentry>
@@ -537,6 +536,13 @@ CREATE INDEX ON films ((lower(title)));
    will choose a name, typically <literal>films_lower_idx</>.)
   </para>
 
+  <para>
+   To create an index with non-default collation:
+<programlisting>
+CREATE INDEX title_idx_german ON films (title COLLATE "de_DE");
+</programlisting>
+  </para>
+
   <para>
    To create an index with non-default sort ordering of nulls:
 <programlisting>

doc/src/sgml/ref/create_type.sgml

@@ -355,10 +355,10 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
   </para>
 
   <para>
-   If the optional
+   If the optional boolean
    parameter <replaceable class="parameter">collatable</replaceable>
    is true, column definitions and expressions of the type may carry
-   collation information and allow the use of
+   collation information through use of
    the <literal>COLLATE</literal> clause.  It is up to the
    implementations of the functions operating on the type to actually
    make use of the collation information; this does not happen