Add support for --enable-exampledir to specify where to place example
files, defaulting to sysconfdir (matching previous behavior).

This is needed to support (cleanly) NetBSD pkgsrc, which requires that
example config files go in $(prefix)/share/examples/pkgname, rather
than in $(prefix)/etc/pkgname.
diff --git a/ospfd/Makefile.am b/ospfd/Makefile.am
index 93b80ae..f687ea9 100644
--- a/ospfd/Makefile.am
+++ b/ospfd/Makefile.am
@@ -32,5 +32,6 @@
 
 EXTRA_DIST = OSPF-MIB.txt OSPF-TRAP-MIB.txt ChangeLog.opaque.txt
 
-dist_sysconf_DATA = ospfd.conf.sample
+examplesdir = $(exampledir)
+dist_examples_DATA = ospfd.conf.sample