Issue with libmongoc.symbols

This file list the experimental features, which break the build without.

— expected-abi 2016-08-08 14:26:05.706963132 +0200
+++ actual-abi 2016-08-08 14:26:05.707963137 +0200
@@ -82,13 +82,11 @@
mongoc_client_pool_pop
mongoc_client_pool_push
mongoc_client_pool_set_apm_callbacks
-mongoc_client_pool_set_appname
mongoc_client_pool_set_error_api
mongoc_client_pool_set_ssl_opts
mongoc_client_pool_try_pop
mongoc_client_select_server
mongoc_client_set_apm_callbacks
-mongoc_client_set_appname
mongoc_client_set_error_api
mongoc_client_set_read_concern
mongoc_client_set_read_prefs
@@ -234,7 +232,6 @@
mongoc_matcher_destroy
mongoc_matcher_match
mongoc_matcher_new
-mongoc_metadata_append
mongoc_rand_add
mongoc_rand_seed
mongoc_rand_status
Makefile:5916: recipe for target 'abicheck' failed

And mongoc_write_concern_is_acknowledged, needed by php extension, should probably be added.