Fix issues found after the review

Author: vitcpp

Diff for: doc/indices.sgm

@@ -69,7 +69,7 @@
           </listitem>
         </itemizedlist>
         <para>
-          GiST index can be also used for quickly finding the points closest to the given one
+          A GiST index can be also used for quickly finding the points closest to the given one
           when ordering by an expression with the <literal>&lt;-&gt;</literal> operator,
           as shown in an example below.
         </para>
@@ -88,7 +88,7 @@
 <![CDATA[VACUUM ANALYZE test;]]>
           </programlisting>
           <para>
-           To find points closest to a given spherical position, use the <literal>&lt;-&gt;</literal> operator:
+           To find the points closest to a given spherical position, use the <literal>&lt;-&gt;</literal> operator:
           </para>
           <programlisting>
 <![CDATA[SELECT * FROM test ORDER BY pos <-> spoint (0.2, 0.3) LIMIT 10 ]]>

Diff for: upgrade_scripts/pg_sphere--1.4.2--1.5.0.sql.in

@@ -1,6 +1,6 @@
 -- Upgrade: 1.4.2 -> 1.5.0
 
-CREATE FUNCTION g_spoint_distance(internal, spoint, smallint, oid, internal)
+CREATE OR REPLACE FUNCTION g_spoint_distance(internal, spoint, smallint, oid, internal)
    RETURNS internal
    AS 'MODULE_PATHNAME', 'g_spoint_distance'
    LANGUAGE 'c';