rocksdb: require less shiny autoconf

precise has 2.59

Signed-off-by: Sage Weil <sage@redhat.com>

diff --git a/src/rocksdb b/src/rocksdb
index 151991550c8eea54d58aff3c33d81a0b6295c9b1..c29e84505e81eb6de6c8feedaef26e08c1c5dc68 160000 (submodule)
--- a/src/rocksdb
+++ b/src/rocksdb
@@ -1 +1 @@
-Subproject commit 151991550c8eea54d58aff3c33d81a0b6295c9b1
+Subproject commit c29e84505e81eb6de6c8feedaef26e08c1c5dc68