modify configure.ac to build sheepdog on rhel5 environment

In our product machine we use rhel5 on 2.6.32-linux-kernel, but sheepdog can't build
on rhel5. It need some modifications to do this.

1. old version autoconf does not support AM_SILENT_RULES() so replace it with check for shell.
2. use SIZEOF_SHORT/INT/LONG instead of AC_TYPE_INT16/32/64.
3. check header files such as sys/eventfd.h sys/signalfd.h etc.
4. use SIZEOF_LONG instead of __SIZEOF_LONG__

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
modify implemention of functions to build sheepdog on rhel5 environment

For using timerfd, eventfd, signalfd, it need to use syscall() instead of glibc's
standard fucntions on rhel5.

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
let logger work on rhel5 environment

In gcc-4.1.2, it dose not support attribute like "constructor(priority)" (it only support
contstructor without 'priority'), so change log_format_register from macro to function and
call it in init_log_formatter() directly.

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>