Start refactoring to reduce executable type knowledge.

courgette/image_info.cc

Index: courgette/image_info.cc
diff --git a/courgette/image_info.cc b/courgette/image_info.cc
index 0c8cdf6038094106d1625c2db61f2ba60e939f09..0f2d9abdff29c1f19fa7b44d0e3a4e36383f706a 100644
--- a/courgette/image_info.cc
+++ b/courgette/image_info.cc
@@ -310,6 +310,14 @@ bool PEInfo::ParseHeader() {
       file_length_ = section_end;
   }
 
+  if (!is_32bit()) {
+    return Bad("64 bit executables are not yet supported");
+  }
+
+  if (!has_text_section()) {
+    return Bad("Resource-only executables are not yet supported");
+  }
+
   failure_reason_ = NULL;
   return true;
 }