Latvian: finally handles PassV2 clauses in a more or less adequate way

Extends the previously introduced support for specifying the verb valence (verb-dependent subject and object cases), involving functions up to PredVP and RelVP.

In Latvian, the passive voice is not used if the agent (subject) is known; to preserve the information structure (i.e. the word order), a clause like 'A is <done> by B' is linearized in the active voice ('A <does> B') where A has the object case (e.g. Acc), and B - the subject case (e.g. Nom). Thus, the verb valence patterns are swapped on-the-fly.

This is still a rather quick & dirty implementation: parameters and linearization types have to be optimized (VerbLav), the use of PassV2 in AdvVP is problematic as it doesn't apply VPSlashPrep / ComplSlash, etc.

lib/src/latvian/ConjunctionLav.gf

@@ -17,7 +17,7 @@ lin
   ConjAdv = conjunctDistrSS ;
 
   ConjNP conj ss = conjunctDistrTable Case conj ss ** {
-    a = toAgr (conjNumber (fromAgr ss.a).n conj.n) (fromAgr ss.a).p (fromAgr ss.a).g ;
+    a = toAgr (conjNumber (fromAgr ss.a).num conj.n) (fromAgr ss.a).pers (fromAgr ss.a).gend ;
     isNeg = False
   } ;