build-sys: fix make distcheck

New distribution package can, and should, now be built using 'make
distcheck' facility from autotools.  Personally I would run the following.

git clean -xdf && git reset --hard HEAD &&
./bootstrap.sh && ./configure && make distcheck

.gitignore

@@ -24,3 +24,5 @@ stamp-h1*
 /version.h.tmp
 
 compile
+
+/mtr-*.tar.gz

Makefile.am

@@ -6,7 +6,7 @@ install-exec-hook:
 	`setcap cap_net_raw+ep $(DESTDIR)$(sbindir)/mtr` \
 	|| chmod u+s $(DESTDIR)$(sbindir)/mtr
 
-mtr_SOURCES = mtr.c \
+mtr_SOURCES = mtr.c mtr.h \
               net.c net.h \
               dns.c dns.h \
               raw.c raw.h \
@@ -16,6 +16,7 @@ mtr_SOURCES = mtr.c \
               getopt.c getopt1.c getopt.h \
               select.c select.h \
               mtr-curses.h \
+              img/mtr_icon.xpm \
               mtr-gtk.h
 
 if IPINFO
@@ -25,7 +26,8 @@ endif
 nodist_mtr_SOURCES = version.h
 EXTRA_mtr_SOURCES = curses.c \
                     gtk.c
-DEFAULT_INCLUDES= $(GLIB_CFLAGS) -I.
+
+mtr_INCLUDES = $(GLIB_CFLAGS) -I$(top_builddir) -I$(top_srcdir)
 mtr_DEPENDENCIES = $(GTK_OBJ) $(CURSES_OBJ)
 mtr_LDFLAGS = $(GTK_OBJ) $(CURSES_OBJ)
 mtr_LDADD = $(GLIB_LIBS) $(RESOLV_LIBS)