build: autotools conversion

build: autotools conversion

1) This removes former Makefiles and install-sh (which is now
   automagically imported via autoreconf).

 Makefile.defs.in
 Makefile.in
 Makefile.rules.in
 src/Makefile.in
 install-sh (now automagically imported via autoreconf).

2) CFLAGS are left almost same, they are integrated into Make_global.am.
   Use AM_CPPFLAGS to set the CFLAGS set by pkgconfig.

3) Add m4 directory to the tree which only contains the .gitignore
   file. Update .gitignore file to skip autogenerated files.

4) include <config.h> whenever required.

5) Minor adjustments to scanner.l and parser_bison.y to compile cleanly
   with autotools.

6) Add %option outfile=lex.yy.c to scanner.l, otherwise I hit this error
   here:

        gcc -DHAVE_CONFIG_H -I. -I..  -I../include -DDEFAULT_INCLUDE_PATH="\"/usr/etc\""  -Wall -Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations -Wdeclaration-after-statement -Wsign-compare -Winit-self -Wformat-nonliteral -Wformat-security -Wmissing-format-attribute -Wcast-align -Wundef -Wbad-function-cast -g -O2 -MT mnl.o -MD -MP -MF $depbase.Tpo -c -o mnl.o mnl.c &&\
        mv -f $depbase.Tpo $depbase.Po
/bin/sh ../build-aux/ylwrap scanner.l lex.yy.c scanner.c -- flex
make[3]: *** [scanner.c] Error 1
make[3]: Leaving directory `/home/pablo/devel/scm/git-netfilter/nftables/src'
make[2]: *** [all] Error 2
make[2]: Leaving directory `/home/pablo/devel/scm/git-netfilter/nftables/src'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/home/pablo/devel/scm/git-netfilter/nftables'
make: *** [all] Error 2

7) Add Makefile.am for include/ (contributed by Giorgio Dal Molin).

The doc/ and files/ conversion to automake will come in follow up
patches but 'make distcheck' already works.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>