Enhance CHECK_EQ and friends to allow extra detail to be appended (like CHECK).

Change-Id: Iaa980892ab31621c8bcca9ea7c6c4ee743333f45
diff --git a/src/zip_archive.cc b/src/zip_archive.cc
index 8c77391..82d97ec 100644
--- a/src/zip_archive.cc
+++ b/src/zip_archive.cc
@@ -222,7 +222,7 @@
     }
   } while (zerr == Z_OK);
 
-  DCHECK(zerr == Z_STREAM_END); // other errors should've been caught
+  DCHECK_EQ(zerr, Z_STREAM_END); // other errors should've been caught
 
   // paranoia
   if (zstream->Get().total_out != uncompressed_length) {