session management: use YAML::Syck for serialization

session management: use YAML::Syck for serialization

When using mysql and a sufficiently recent version
of DBD::mysql that actually respects the mysql_enable_utf8
option, setting the current branch to a name that
includes a diacritic causes the session to fail
and forces the user to the login screen upon
clicking another link.

This turned out to be due to the default (Data::Dumper)
serialization used by CGI::Session, which truncated the
session object at the diacritic.  By enabling
that module's YAML serialization option, the problem
was resolved.

This patch introduces a dependency on the YAML::Syck
module.

Signed-off-by: Chris Cormack <crc@liblime.com>
Signed-off-by: Joshua Ferraro <jmf@liblime.com>