add "--enable-plugins" to configure, and also "UCONFIG_ENABLE_PLUGINS". These are disabled by default. Also, start splitting out acinclude.m4 content to source/config/m4/.. X-SVN-Rev: 37675
X-SVN-Rev: 27600
(specifically, r26808:27031 of http://source.icu-project.org/repos/icu/icu/branches/srl/dll6633 and then r27117 r27118 r27119 r27121 r27137 r27139 r27159 r27160 r27172 r27173 r27181 r27182 ) X-SVN-Rev: 27195