Back-patch fixes to make TAP tests work on Windows.

This back-ports commit 13d856e177 and assorted followon patches
into 9.4 and 9.5.  9.5 and HEAD are now substantially identical in all
the files touched by this commit, except that 010_pg_basebackup.pl has
a few more tests related to the new --slot option.  9.4 has many fewer
TAP tests, but the test infrastructure files are substantially the same,
with the exception that 9.4 lacks the single-tmp-install infrastructure
introduced in 9.5 (commit dcae5facca).

The primary motivation for this patch is to ensure that TAP test case
fixes can be back-patched without hazards of the kind seen in commits
34557f544/06dd4b44f.  In principle it should also make the world safe
for running the TAP tests in the buildfarm in these branches; although
we might want to think about back-porting dcae5facca to 9.4 if
we're going to do that for real, because the TAP tests are quite disk
space hungry without it.

Michael Paquier did the back-porting work; original patches were by
him and assorted other people.

doc/src/sgml/install-windows.sgml

@@ -438,6 +438,7 @@ $ENV{CONFIG}="Debug";
 <userinput>vcregress contribcheck</userinput>
 <userinput>vcregress ecpgcheck</userinput>
 <userinput>vcregress isolationcheck</userinput>
+<userinput>vcregress tapcheck</userinput>
 <userinput>vcregress upgradecheck</userinput>
 </screen>
 
@@ -450,6 +451,29 @@ $ENV{CONFIG}="Debug";
    For more information about the regression tests, see
    <xref linkend="regress">.
   </para>
+
+  <para>
+   Running the TAP regression tests, with "vcregress tapcheck", requires an
+   additional Perl module to be installed:
+   <variablelist>
+    <varlistentry>
+     <term><productname>IPC::Run</productname></term>
+     <listitem><para>
+      As of this writing, <literal>IPC::Run</> is not included in the
+      ActiveState Perl installation, nor in the ActiveState Perl Package
+      Manager (PPM) library. To install, download the
+      <filename>IPC-Run-&lt;version&gt;.tar.gz</> source archive from CPAN,
+      at <ulink url="http://search.cpan.org/dist/IPC-Run/"></>, and
+      uncompress. Edit the <filename>buildenv.pl</> file, and add a PERL5LIB
+      variable to point to the <filename>lib</> subdirectory from the
+      extracted archive. For example:
+<programlisting>
+$ENV{PERL5LIB}=$ENV{PERL5LIB} . ';c:\IPC-Run-0.94\lib';
+</programlisting>
+     </para></listitem>
+    </varlistentry>
+   </variablelist>
+  </para>
  </sect2>
 
  <sect2>