Set {NDIFF,NPING,ZENMAP}DIR in configure.ac and substitute it in the Makefile

instead of having the directory names in Makefile.in.  This is how most
everything else works: Ncat (NCATDIR), liblua (LIBLUADIR), etc.

Makefile.in

@@ -28,9 +28,9 @@ STRIP = @STRIP@
 LIBPCAPDIR = @libpcapdir@
 LIBPCREDIR = @LIBPCREDIR@
 export LIBDNETDIR = @LIBDNETDIR@
-ZENMAPDIR = zenmap
-NDIFFDIR = ndiff
-NPINGDIR = nping
+ZENMAPDIR = @ZENMAPDIR@
+NDIFFDIR = @NDIFFDIR@
+NPINGDIR = @NPINGDIR@
 PYTHON = @PYTHON@
 DEFS = @DEFS@ -DNMAP_NAME=\"$(NMAP_NAME)\" -DNMAP_URL=\"$(NMAP_URL)\" -DNMAP_PLATFORM=\"$(NMAP_PLATFORM)\" -DNMAPDATADIR=\"$(nmapdatadir)\"
 # With GCC, add extra security checks to source code.

configure.ac

@@ -195,6 +195,8 @@ dnl If any socket libraries needed
 AC_SEARCH_LIBS(setsockopt, socket)
 AC_SEARCH_LIBS(gethostbyname, nsl)
 
+NDIFFDIR=ndiff
+
 # Do they want Ndiff?
 AC_ARG_WITH(ndiff, AC_HELP_STRING([--without-ndiff], [Skip installation of the Ndiff utility]), [], [with_ndiff=check])
 
@@ -218,11 +220,14 @@ else
   NDIFF_CLEAN=ndiff_clean
   NDIFF_DIST_CLEAN=ndiff_dist_clean
 fi
+AC_SUBST(NDIFFDIR)
 AC_SUBST(BUILDNDIFF)
 AC_SUBST(INSTALLNDIFF)
 AC_SUBST(NDIFF_CLEAN)
 AC_SUBST(NDIFF_DIST_CLEAN)
 
+ZENMAPDIR=zenmap
+
 # Do they want Zenmap?
 AC_ARG_WITH(zenmap, AC_HELP_STRING([--without-zenmap], [Skip installation of the Zenmap graphical frontend]), [], [with_zenmap=check])
 
@@ -248,12 +253,15 @@ else
   ZENMAP_CLEAN=zenmap_clean
   ZENMAP_DIST_CLEAN=zenmap_dist_clean
 fi
+AC_SUBST(ZENMAPDIR)
 AC_SUBST(BUILDZENMAP)
 AC_SUBST(INSTALLZENMAP)
 AC_SUBST(UNINSTALLZENMAP)
 AC_SUBST(ZENMAP_CLEAN)
 AC_SUBST(ZENMAP_DIST_CLEAN)
 
+NPINGDIR=nping
+
 # Do they want Nping?
 AC_ARG_WITH(nping, AC_HELP_STRING([--without-nping], [Skip installation of the Nping utility]), [], [with_nping=check])
 
@@ -271,6 +279,7 @@ else
   NPING_DIST_CLEAN=nping_dist_clean
   AC_CONFIG_SUBDIRS(nping)
 fi
+AC_SUBST(NPINGDIR)
 AC_SUBST(BUILDNPING)
 AC_SUBST(INSTALLNPING)
 AC_SUBST(UNINSTALLNPING)