Low: libcrmcommon: compare CRM_meta_ properly

Previously, when filtering XML attributes for digests, we would filter
attributes starting with "CRM_meta" case-insensitively. Now, compare
against "CRM_meta_" case-sensitively.

This could potentially cause resource restarts after upgrading to a version
with this commit, for any resource that has instance attributes that start with
something like "crm_meta" -- a highly unlikely scenario.