Preprocessor rebase

– PAC model: fixes to M_.pac.MODEL.ar (information about autoregressive part)
  + Fix order of items in this structure. Previously, items were ordered
    according to the declaration order of parameters. Now, items are order
    according to lag order (first lag appears first)
  + Gracefully handle the case where there is no autoregressive part
    (Ref. Dynare/preprocessor#52)
– Block decomposition:
  + bugfix for solve one boundary blocks with mfs>0
  + fix evaluation of recursive variables in solved blocks
  (Ref. Dynare/dynare#1726)
— Fix various potential bugs with model local variable
— Ensure that negative constants are never marked as temporary terms

By the way, activate tests/pac/trend-component-31/example.mod, since it should
now work.

preprocessor

@@ -1 +1 @@
-Subproject commit 8bfcc59af7331621e534c8ff58eb5afeadb070fe
+Subproject commit 58a35214c3e5b421baca532443efd089f3255a3c

tests/Makefile.am

@@ -504,6 +504,7 @@ ECB_MODFILES = \
 	pac/trend-component-29/example2.mod \
 	pac/trend-component-29/example2.mod \
 	pac/trend-component-30/example.mod \
+	pac/trend-component-31/example.mod \
 	write/example1.mod \
 	ecb/backward-models/irf/solow_1.mod \
 	ecb/backward-models/irf/solow_2.mod \

tests/pac/trend-component-31/example.mod

@@ -1,5 +1,7 @@
 // --+ options: json=compute, stochastic +--
 
+// Regression test for bug preprocessor#52
+
 var x1 x2 x1bar x2bar z ;
 
 varexo ex1 ex2 ex1bar ex2bar ez ;