put in an auto* check for the path to perl (if it exists), and modified

* configure.in, Makefile.am: put in an auto* check for the
  path to perl (if it exists), and modified make Timingtests
  to use that path instead of just executing the dbgenattr.pl
  script (bug 148056)
diff --git a/Makefile.am b/Makefile.am
index 34ca3b5..d38bb2b 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -757,7 +757,7 @@
 
 $(srcdir)/dba100000.xml: dbgenattr.pl
 	@echo "## generating dba100000.xml"
-	@($(top_srcdir)/dbgenattr.pl 100000 > $(srcdir)/dba100000.xml)
+	@($(PERL) $(top_srcdir)/dbgenattr.pl 100000 > $(srcdir)/dba100000.xml)
 
 Timingtests: xmllint$(EXEEXT) $(srcdir)/dba100000.xml
 	@echo "## Timing tests to try to detect performance"