php_mongo_dbref_resolve_id() is declared as TSRM aware function.. you must pass TSRMLS_CC to it.

This breaks the Travis builds:
/home/travis/build/mongodb/mongo-php-driver/collection.c:1454:3: error: too few arguments to function ‘php_mongo_dbref_resolve_id’
/home/travis/build/mongodb/mongo-php-driver/types/db_ref.h:35:7: note: declared here

Which is why none of the tests are executed, failing with "Unable to load dynamic library .. mongo.so".

We should maybe fix that script to bail out from compile.sh on build failures to make it more obvious...