Merge branch 'ah/autoconf-fixes'

"./configure --with-expat=no" did not work as a way to refuse use of the expat library on a system with the library installed, which has been corrected. * ah/autoconf-fixes: configure.ac: always save NO_ICONV to config.status configure.ac: don't overwrite NO_CURL option configure.ac: don't overwrite NO_EXPAT option