util::zip reform. + Use '::zipfile::mkzip', introduced in tcllib 1.18, if available. + For unix-like systems, with older tcllib versions, bash was used for changing directories. This method was problematic when using certain characters for the filenames, such as backticks, for example. In order to avoid this and properly quote everything, we use tclsh instead, in a convoluted and funny way (thanks to Nathan Coulter for the hack). + TODO: test this method also on windows, and unify the legacy implementations if it works.