Let it install correctly when built via phpize

ext/pdo/Makefile.frag

@@ -8,7 +8,11 @@ install-pdo-headers:
 	echo "Installing PDO headers:          $(INSTALL_ROOT)$(phpincludedir)/ext/pdo/"
 	$(mkinstalldirs) $(INSTALL_ROOT)$(phpincludedir)/ext/pdo
 	for f in $(PDO_HEADER_FILES); do \
-		if test -f "$(top_srcdir)/ext/pdo/$$f"; then \
+		if test -f "$(top_srcdir)/$$f"; then \
+			$(INSTALL_DATA) $(top_srcdir)/$$f $(INSTALL_ROOT)$(phpincludedir)/ext/pdo; \
+		elif test -f "$(top_builddir)/$$f"; then \
+			$(INSTALL_DATA) $(top_builddir)/$$f $(INSTALL_ROOT)$(phpincludedir)/ext/pdo; \
+		elif test -f "$(top_srcdir)/ext/pdo/$$f"; then \
 			$(INSTALL_DATA) $(top_srcdir)/ext/pdo/$$f $(INSTALL_ROOT)$(phpincludedir)/ext/pdo; \
 		elif test -f "$(top_builddir)/ext/pdo/$$f"; then \
 			$(INSTALL_DATA) $(top_builddir)/ext/pdo/$$f $(INSTALL_ROOT)$(phpincludedir)/ext/pdo; \