conf: use better clang detection

Handle case where compiler isn't called 'clang'. This is slightly
modified from the version here:
http://src.chromium.org/svn/branches/1312/src/third_party/mesa/MesaLib/configure.ac

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
autoconf: add check for the boost_program_options library

check for the existence of boost_program_options library in
configure.ac since several files need that library

Signed-off-by: Xing Lin <xinglin@cs.utah.edu>
automake: replaced hardcoded '-lboost_program_options' with a macro

replaced '-lboost_program_options' with the BOOST_PROGRAM_OPTIONS_LIBS
macro in related Makefile.am files

Signed-off-by: Xing Lin <xinglin@cs.utah.edu>
Merge pull request #829 from ceph/port/detect-clang

conf: use better clang detection
Merge pull request #838 from xinglin/boost-program-option-check

autoconf: add check for the boost_program_options library

Reviewed-by: Noah Watkins <noah.watkins@inktank.com>
Merge git://github.com/ceph/ceph