Install pg_isolation_regress and isolationtester

We already install assorted tools for testing extensions, but these two
were missing.  Having them installed, and after ISOLATION support was
added to PGXS's  makefiles by d3c09b9b13, helps third-party modules
usefully include isolation tests.  Compare c3a0818460.

Author: Craig Ringer <craig.ringer@enterprisedb.com>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/CAMsr+YFsCMH3B4uOPFE+2qWM6k=o=hf9LGiPNCfwqKdUPz_BsQ@mail.gmail.com

src/test/isolation/Makefile

@@ -18,12 +18,16 @@ OBJS = \
 
 all: isolationtester$(X) pg_isolation_regress$(X)
 
-# Though we don't install these binaries, build them during installation
-# (including temp-install).  Otherwise, "make -j check-world" and "make -j
-# installcheck-world" would spawn multiple, concurrent builds in this
-# directory.  Later builds would overwrite files while earlier builds are
-# reading them, causing occasional failures.
-install: | all
+install: all installdirs
+	$(INSTALL_PROGRAM) pg_isolation_regress$(X) '$(DESTDIR)$(pgxsdir)/$(subdir)/pg_isolation_regress$(X)'
+	$(INSTALL_PROGRAM) isolationtester$(X) '$(DESTDIR)$(pgxsdir)/$(subdir)/isolationtester$(X)'
+
+installdirs:
+	$(MKDIR_P) '$(DESTDIR)$(pgxsdir)/$(subdir)'
+
+uninstall:
+	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/pg_isolation_regress$(X)'
+	rm -f '$(DESTDIR)$(pgxsdir)/$(subdir)/isolationtester$(X)'
 
 submake-regress:
 	$(MAKE) -C $(top_builddir)/src/test/regress pg_regress.o