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/vtysh/Makefile.am b/vtysh/Makefile.am
index b5f964e..95f8f7f 100644
--- a/vtysh/Makefile.am
+++ b/vtysh/Makefile.am
@@ -12,9 +12,10 @@
 noinst_HEADERS = vtysh.h vtysh_user.h
 vtysh_LDADD = ../lib/libzebra.a @LIBCAP@
 
-sysconf_DATA = vtysh.conf.sample
+examplesdir = $(exampledir)
+dist_examples_DATA = vtysh.conf.sample
 
-EXTRA_DIST = extract.pl vtysh.conf.sample
+EXTRA_DIST = extract.pl
 
 rebuild4:
 	./extract.pl $(top_srcdir)/zebra/*.c $(top_srcdir)/ripd/*.c $(top_srcdir)/ospfd/*.c $(top_srcdir)/bgpd/*.c $(top_srcdir)/lib/keychain.c $(top_srcdir)/lib/routemap.c $(top_srcdir)/lib/filter.c $(top_srcdir)/lib/plist.c $(top_srcdir)/lib/distribute.c $(top_srcdir)/lib/if_rmap.c > vtysh_cmd.c