Make vtysh work on NetBSD, and minor cleanups:

  if --enable-vtysh, look for perl, and substitute into vtysh/extract.pl,
  rather than assuming perl is in /usr/bin

  Look for tputs in libtermcap and libcurses, in addition to
  previously-searched locations.  Follow GNU readlines search order.

  Clean up --enable-vtysh definition in configure.ac.

  Add vtysh/vtysh_cmds.c to CLEANFILES.  This is important if
  extract.pl fails, so that 'make clean && make' will regenerate
  vtysh_cmds.c rhather than using the old zero-length file.
diff --git a/vtysh/Makefile.am b/vtysh/Makefile.am
index 9118350..fea0cb0 100644
--- a/vtysh/Makefile.am
+++ b/vtysh/Makefile.am
@@ -9,6 +9,7 @@
 
 vtysh_SOURCES = vtysh_main.c vtysh.c vtysh_user.c vtysh_config.c
 nodist_vtysh_SOURCES = vtysh_cmd.c
+CLEANFILES = vtysh_cmd.c
 noinst_HEADERS = vtysh.h vtysh_user.h
 vtysh_LDADD = ../lib/libzebra.a @LIBCAP@