Add the signal catcher (for SIGQUIT and SIGUSR1).

Also fix some of the thread implementation.

Change-Id: If2d1b59a149ba1ac192ad9bc74319c8dff228549
diff --git a/src/utils.h b/src/utils.h
index e52f476..b5210ec 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -163,6 +163,9 @@
 
 std::string ReadFileToString(const char* file_name);
 
+// Returns the current date in ISO yyyy-mm-dd hh:mm:ss format.
+std::string GetIsoDate();
+
 }  // namespace art
 
 #endif  // ART_SRC_UTILS_H_