Make sure sharedir/extension/ directory is created when needed.

The previous coding worked as long as MODULEDIR wasn't set explicitly,
because we create sharedir/$(datamoduledir) and the default value of
that is "extension".  But if some other value is specified for MODULEDIR
then the installation directory needed for the control file wasn't made.

Cédric Villemain

src/makefiles/pgxs.mk

@@ -146,6 +146,9 @@ endif # MODULE_big
 
 
 installdirs:
+ifneq (,$(EXTENSION))
+	$(MKDIR_P) '$(DESTDIR)$(datadir)/extension'
+endif
 ifneq (,$(DATA)$(DATA_built))
 	$(MKDIR_P) '$(DESTDIR)$(datadir)/$(datamoduledir)'
 endif