Travis: quell warnings about different API and schema versions

Yes, I *know* Compara, ontology and Variation schemas are still 98. It's
not that it could just happen, test databases have to be explicitly
patched - and in any case with Infra being at present the only team
which bumps versions to N+1 right after the branching of release/N
rather than just before the branching of release/N+1, it is only to be
expected. And call me weird but I like Test::Warnings tests to catch
warnings which really ARE unexpected.

.travis.yml

@@ -40,6 +40,10 @@ install:
   - cp travisci/MultiTestDB.conf.travisci.SQLite modules/t/MultiTestDB.conf.SQLite
   - mysql -u root -h localhost -e 'GRANT ALL PRIVILEGES ON *.* TO "travis"@"%"'
 
+before_script:
+  # This should probably be removed on release branches
+  - touch "$HOME/.ensemblapi_no_version_check"
+
 script: "./travisci/harness.sh"
 
 jobs: