- Enable curl and rsync support

- update to 2.6.13:
- fixed compilation warning in testing routine (outside libdar and dar)
- due to change in autoconf, the --sysconfdir path (which defaults to
${prefix}/etc) was read as an empty string, leading dar to look for
darrc system file at the root of the filesystem (/darrc)
- fixed bug that should occur in extremely rare conditions (it has been
discover during 2.7.0 validation process): compression must be used,
no ciphering, no hashing, file changed at backup time or had a poor
compression ratio, was not saved at slice boundary, the previous
entry had an EA saved but no FSA or an unchanged FSA. In such
conditions are all met, dar tries to resave the file in place, but
partially or totally overwites the EAs of the previous entry leading
to archive testing to fail for these EA (though the archive could be
finished without error).
- fixed bug met when case insensitive mask is requested (-an option)
and locale of file to restore or backup is not the one the dar binary
is run with.