Fix: bump minimal urcu dependency to 0.11

Fix: bump minimal urcu dependency to 0.11

cds_lfht_destroy is used from within RCU read-side critical sections
which is only allowed for urcu >= 0.10 (see userspace-rcu commit
d0ec0ed2f).

Such uses were introduced as part of the 2.11 release (contemporary
to urcu 0.10).

This version of the fix differs from 879000628 since the configure
script has changed significantly for the 2.13 release (use of PKG_CONFIG
rather than looking for a version-specific symbol).

The configure script looks for `urcu_memb_barrier` which was introduced
in liburcu 0.11.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I7d8daba877cbdcfaf93cdc4c9b16a3b3df974782