[plugin_installer] do not update plugin if it's not compatible with current Gajim version. Fixes #225

Show a warning when download fails in all cases

Fix downloading plugins

BoySka authored 8 years ago and Yann Leboulanger committed 8 years ago

Only TLS >= v1.2 allowed, with no compression (we don't need it, as we
are only downloading zipfiles)

this also has improvements about cert verification: urllib2 supports
subjectAltNames, which ssl+ftplib does not.

create one ConfigParser instance per file so old values ore not used if current manifest has missing fields. Check that manifest file is full