More SIGQUIT handling, various Thread fixes.

Change-Id: I3233c300d1c838c2eee0ba9be6018b7fbd907386
diff --git a/src/image_test.cc b/src/image_test.cc
index fd88b20..b205fe2 100644
--- a/src/image_test.cc
+++ b/src/image_test.cc
@@ -74,7 +74,8 @@
   // enable to display maps to debug boot_base and boot_limit checking problems below
   if (false) {
     const char* maps_file = "/proc/self/maps";
-    std::string contents = ReadFileToString(maps_file);
+    std::string contents;
+    CHECK(ReadFileToString(maps_file, &contents));
     LG << maps_file << ":\n" << contents;
   }