Fix several bugs 修复数个问题

* 修复 同时安装两个内核会导致update-burg生成错误 问题
Fix bug that update-burg outputs inproperly when 2 kernels are
installed at the same time
Firef0x/burg#9 https://github.com/Firef0x/burg/issues/9

* 修复 grub-mkfont.c 中的 ftsynth.h引用路径 错误问题
Correct the file path of ftsynth.h in grub-mkfont.c
Firef0x/burg#8

* 改写 10_linux.in, 30_os-prober.in, grub-mkconfig_lib.in，使用 gettext
处理某些字符串
Rewrite 10_linux.in, 30_os-prober.in, grub-mkconfig_lib.in, use
gettext to handle some strings
Firef0x/burg#4 https://github.com/Firef0x/burg/issues/4
Firef0x/burg#11 https://github.com/Firef0x/burg/issues/11

* 30_os-prober.in 增加识别 Windows Server 2008
Add judge for Windows Server 2008 in 30_os-prober.in