Add Synonym Check to Taxonomy Mappings

We want to map incoming feeds to a taxonomy whose terms frequently use synonyms to show preferred terms. Naturally, if a term coming in from the feed already exists in the vocabulary as a synonym, we want to use the preferred, already-exisiting taxonomy term and not add a brand new term that effectively replicates something that semantically already exists in the vocabulary.

The attached patch seems to achieve this by modifying mappers/feedapi_mapper_taxonomy.inc to add to the current terms any taxonomy terms where an incoming keyword matches an existing synonym.

Comments/corrections appreciated.