Match: show better error message if template throws

lib/bemxjst/match.js

@@ -153,6 +153,19 @@ Match.prototype.tryCatch = function(fn, ctx) {
     return fn.call(ctx, ctx, ctx.ctx);
   } catch (e) {
     this.thrownError = e;
+    if (this.modeName) {
+      this.thrownError.ctx = ctx;
+      this.thrownError.name = 'BEMXJST ERROR';
+      var classBuilder = this.entity.bemxjst.classBuilder;
+
+      var cause = e.stack.split('\n')[1];
+      this.thrownError.message = 'Template error in mode ' +
+            this.modeName + ' in block ' +
+            classBuilder.build(ctx.ctx.block, ctx.ctx.elem) +
+            '\n    ' + e.message + '\n';
+      this.thrownError.stack = this.thrownError.name + ': ' +
+            this.thrownError.message + ' ' + cause + '\n' + e.stack;
+    }
   }
 };