Update .merlin warnings list and compile flags

Summary:public
Bring merlin config in sync with makefile, in particular so that it can
find values and types in Utils, and so that it reports the same warnings.

Reviewed By: jvillard, cristianoc

Differential Revision: D2959425

fb-gh-sync-id: 9e7b443
shipit-source-id: 9e7b443

infer/.merlin

@@ -1,4 +1,14 @@
 S src/**
 B _build-infer/**
-PKG sawja
 PKG atdgen
+PKG extlib
+PKG javalib
+PKG ptrees
+PKG sawja
+PKG str
+PKG unix
+PKG yojson
+PKG zip
+FLG -open Utils
+FLG -principal -safe-string -short-paths -strict-formats -strict-sequence
+FLG -w +a-4-9-40-41-42-45-48-50