Docs: tidy up various usages of the productname tag

This tries to bring a bit more consistency to the use of the <productname>
tag in the documents.  This fixes a couple of mistakes with our own
product.  We definitely should be consistently calling that PostgreSQL
when we're referring to the modern-day version of the software.

This also tidies up a couple of inconsistencies with the case of other
product names, namely Emacs and Python.  We also get rid of some incorrect
usages of <productname> and replace them with <literal>.

Many of these mistakes exist in the back branches, but they don't quite
seem critical enough to warrant fixing them in prior versions at this
stage.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20220411020336.GB26620@telsasoft.com

doc/src/sgml/catalogs.sgml

@@ -12962,7 +12962,7 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
   <para>
    The <structname>pg_shmem_allocations</structname> view shows allocations
    made from the server's main shared memory segment.  This includes both
-   memory allocated by <productname>postgres</productname> itself and memory
+   memory allocated by <productname>PostgreSQL</productname> itself and memory
    allocated by extensions using the mechanisms detailed in
    <xref linkend="xfunc-shared-addin" />.
   </para>

doc/src/sgml/client-auth.sgml

@@ -1523,7 +1523,7 @@ omicron         bryanh                  guest1
    </note>
 
    <para>
-    The following configuration options are supported for <productname>ident</productname>:
+    The following configuration options are supported for <literal>ident</literal>:
     <variablelist>
      <varlistentry>
       <term><literal>map</literal></term>
@@ -1597,7 +1597,7 @@ omicron         bryanh                  guest1
    </para>
 
    <para>
-    The following configuration options are supported for <productname>peer</productname>:
+    The following configuration options are supported for <literal>peer</literal>:
     <variablelist>
      <varlistentry>
       <term><literal>map</literal></term>

doc/src/sgml/ecpg.sgml

@@ -8233,7 +8233,7 @@ $COMMIT;
    you functions that have the same name and the same basic behavior but it is
    no drop-in replacement if you are using <productname>Informix</productname> at the moment. Moreover,
    some of the data types are different. For example,
-   <productname>PostgreSQL's</productname> datetime and interval types do not
+   <productname>PostgreSQL</productname>'s datetime and interval types do not
    know about ranges like for example <literal>YEAR TO MINUTE</literal> so you won't
    find support in ECPG for that either.
   </para>

doc/src/sgml/install-windows.sgml

@@ -370,7 +370,7 @@ $ENV{MSBFLAGS}="/m";
   </para>
 
   <para>
-   To use a server-side third party library such as <productname>python</productname> or
+   To use a server-side third party library such as <productname>Python</productname> or
    <productname>OpenSSL</productname>, this library <emphasis>must</emphasis> also be
    64-bit. There is no support for loading a 32-bit library in a 64-bit
    server. Several of the third party libraries that PostgreSQL supports may

doc/src/sgml/sources.sgml

@@ -63,7 +63,7 @@
 
    <para>
     The <filename>src/tools/editors</filename> directory contains sample settings
-    files that can be used with the <productname>emacs</productname>,
+    files that can be used with the <productname>Emacs</productname>,
     <productname>xemacs</productname> or <productname>vim</productname>
     editors to help ensure that they format code according to these
     conventions.