rrdtool/lynx:
 * don't cache and don't use cached values of ac_cv_func_acos, ac_cv_lib_m_acos variables
 * expected to fix/workaround build problems reported in #1922, #2115
 * refs #1922, #2115, #1804


git-svn-id: file:///var/svn/freetz/trunk@10586 149334a1-2f27-0410-a3b9-fc62619ac1e6