Issue with Perl dependency for Xref Mapping pipeline

[sgiorgetti]

Issue with Perl dependency XML::LibXML

THIS APPLIES TO Xref Mapping ONLY AND DOES NOT APPLY TO the "core API"

The test suite of XML::LibXML is incompatible with some versions of libxml2 - possibly from libxml2 2.13.0.
This cause a few tests to fail, preventing the installation of the module using the standard cpanfile from this repo.

From shlomif/perl-XML-LibXML#87 it looks like being an issue with the test suite only, but there is also a backward compatibility concern from perl-XML-LibXML's author, still under investigation.
Not sure when the PR will be merged.

Temporary proposed (ugly) solution

Force install XML::LibXML before installing Ensembl dependencies.
For instance by issuing cpanm -v --force XML::LibXML
Or to save time and hoping for the best: cpanm --notest XML::LibXML

Temporary proposed (ugly) solution no. 2

Rollback libxml2 to a version prior to 2.13.0 ... and dealing with collateral damage