Enable automake silent rules and other improvements

__English:__
* d1e469c adds `bootstrap.sh` and `autogen.sh` which can be used to regenerate the autotools created files and, in the case of `autogen.sh` invoke configure with a default set of parameters (usually the ones the maintainer wants). I found that these were necessary to have for MinGW as the current `automake 1.11.6` and `autoconf 2.69` generated version didn't work, and they had to be re-generated.
* 92da24a adds and enables silent build rules by default, which, besides being much nicer, allows makes compilation errors and warnings an lot more explicit. See example of output at the end. The old verbose mode can still be re-enabled at any time by using `make V=1` (or `--disable-silent-rules` when invoking configure). In this commit, only `configure.ac` and `stage2/Makefile.am` were manually modified. The other files were generated by running `bootstrap.sh`.
* 92da24a and 2384551 are straightforward and fix a handful of warnings that are reported on MinGW.

__中文__ (using google translate)
* d1e469c 添加`bootstrap.sh`和可用于再生的自动工具创建的文件`autogen.sh`和，在的情况下`autogen.sh`调用配置用的参数（通常是那些维护者想要一组默认的）。我发现，这些是必要的，对MinGW的为当前`automake 1.11.6`和`autoconf 2.69`生成的版本没有工作，他们不得不重新生成。
* 92da24a 增加，使默认情况下，它除了是好多了，可以让编译错误和警告的很多更明确的沉默生成规则。看到在最后的例子输出。老详细模式仍然可以重新启用在任何时候使 `make V=1`（或 `./configure  --disable-silent-rules`）。在这个承诺中，只有`configure.ac`和``stage2/ Makefile.am`进行手动修改。通过运行`bootstrap.sh`生成的其它文件。
* 92da24a 和 2384551 顷简单，解决少数被报道MinGW的警告。

__Example of a build with silent rules enabled:__
```
$ make
make  all-recursive
make[1]: Entering directory `/d/grub4dos'
Making all in stage2
make[2]: Entering directory `/d/grub4dos/stage2'
  CPPAS  pre_stage2_exec-asm.o
  CC     pre_stage2_exec-bios.o
  CC     pre_stage2_exec-boot.o
  CC     pre_stage2_exec-builtins.o
  CC     pre_stage2_exec-char_io.o
  CC     pre_stage2_exec-cmdline.o
  CC     pre_stage2_exec-common.o
  CC     pre_stage2_exec-console.o
  CC     pre_stage2_exec-dec_lzma.o
  CC     pre_stage2_exec-disk_io.o
  CC     pre_stage2_exec-fsys_ext2fs.o
  CC     pre_stage2_exec-fsys_fat.o
  CC     pre_stage2_exec-fsys_ntfs.o
  CC     pre_stage2_exec-fsys_ffs.o
  CC     pre_stage2_exec-fsys_iso9660.o
  CC     pre_stage2_exec-fsys_jfs.o
  CC     pre_stage2_exec-fsys_minix.o
  CC     pre_stage2_exec-fsys_reiserfs.o
  CC     pre_stage2_exec-fsys_ufs2.o
  CC     pre_stage2_exec-fsys_vstafs.o
  CC     pre_stage2_exec-fsys_xfs.o
  CC     pre_stage2_exec-fsys_pxe.o
  CC     pre_stage2_exec-fsys_initrd.o
  CC     pre_stage2_exec-fsys_fb.o
  CC     pre_stage2_exec-gunzip.o
  CC     pre_stage2_exec-hercules.o
  CC     pre_stage2_exec-md5.o
  CC     pre_stage2_exec-serial.o
  CC     pre_stage2_exec-stage2.o
  CC     pre_stage2_exec-terminfo.o
  CC     pre_stage2_exec-tparm.o
  CC     pre_stage2_exec-graphics.o
  CCLD   pre_stage2.exec.exe
  OBJ    pre_stage2
  CPPAS  dosstart_exec-dosstart.o
  CCLD   dosstart.exec.exe
  CPPAS  badgrubstart_exec-badgrubstart.o
  CCLD   badgrubstart.exec.exe
  CPPAS  grldrstart_exec-grldrstart.o
  CCLD   grldrstart.exec.exe
  CPPAS  mbrstart_exec-mbrstart.o
  CCLD   mbrstart.exec.exe
  CPPAS  bootlacestart_exec-bootlacestart.o
  CCLD   bootlacestart.exec.exe
  CPPAS  hmloadstart_exec-hmloadstart.o
  CCLD   hmloadstart.exec.exe
  OBJ    dosstart
  GEN    grub.exe
  OBJ    badgrubstart
  GEN    badgrub.exe
  OBJ    grldrstart
  GEN    grldr
  OBJ    mbrstart
  GEN    grldr.mbr
  OBJ    bootlacestart
  GEN    bootlace.com
  OBJ    hmloadstart
  GEN    hmload.com
                       Ultimate Packer for eXecutables
                          Copyright (C) 1996 - 2013
UPX 3.91w       Markus Oberhumer, Laszlo Molnar & John Reiser   Sep 30th 2013

        File size         Ratio      Format      Name
   --------------------   ------   -----------   -----------
      6140 ->      1712   27.88%     dos/sys     eltorito.sys

Packed 1 file.
make[2]: Leaving directory `/d/grub4dos/stage2'
make[2]: Entering directory `/d/grub4dos'
make[2]: Nothing to be done for `all-am'.
make[2]: Leaving directory `/d/grub4dos'
make[1]: Leaving directory `/d/grub4dos'
```