MedSLT almost fully converted to AFF

I've made a lot of progress this week on converting the bidirectional English/Spanish version of MedSLT to AFF format. I've parameterized the Spanish system to support AFF representations, and added AFF versions of most of the necessary config file and scripts. In particular,

• You can build a full AFF version of Spa by doing 'make role_marked' in Spa/scripts.
• You can run interactive bidirectional AFF Eng/Spa text systems using the files load_bidirectional_role_marked.pl and load_bidirectional_restricted_role_marked.pl in EngSpa/scripts.
  
• There are targets in EngSpa/scripts/Makefile for running AFF versions of the QA corpus, both plain and restricted, with the obvious naming conventions.

I've done preliminary testing, and everything should be checked in. There are still things missing, e.g. nothing so far in Spa/Spa for checking back-translation, but I figured it would be best at this point to hand over to Pierrette, so that she can refine the rules. I've only made some absolutely minimal changes, enough to check that a few sentences go through.

When this piece of work is finished, all of MedSLT should be available in AFF format, which means that we'll be able to retire the old linear version and only support one system. I'm hopeful that build times will then be low enough for us to go back to building and testing the system every night, as we used to do.