Fix a typo in the configure.in rules that prevented tracetop from being
installed.

Reported upstream as: http://www.wand.net.nz/trac/libtrace/ticket/312
Index: configure.in
===================================================================
--- /configure.in	(revision 1701)
+++ /configure.in	(working copy)
@@ -494,7 +495,7 @@
 AM_CONDITIONAL([HAVE_NETPACKET_PACKET_H], [test "$libtrace_netpacket_packet_h" = true])
 AM_CONDITIONAL([HAVE_LIBGDC], [test "$ac_cv_header_gdc_h" = yes])
 AM_CONDITIONAL([HAVE_LLVM], [test "x$JIT" != "xno" ])
-AM_CONDITIONAL([HAVE_NCURSES], [test "$xhave_ncurses" = "xyes"])
+AM_CONDITIONAL([HAVE_NCURSES], [test "x$have_ncurses" = "xyes"])
 
 # Check for miscellaneous programs
 AC_CHECK_PROG([libtrace_doxygen], [doxygen], [true], [false])
