Enable "cert-err34-c" tidy checks.

Now that we've moved to Binder, we only have a few lingering atoi()
usages that are cleaned up in this CL.

Rewrite match_multi_entry() entirely, with tests to verify both old
and new implementations.

Test: adb shell /data/nativetest/vold_tests/vold_tests
Bug: 36655947
Change-Id: Ib79dc1ddc2366db4d5b4e1a1e2ed9456a06a983e
diff --git a/cryptfs.h b/cryptfs.h
index a7b650f..2169f54 100644
--- a/cryptfs.h
+++ b/cryptfs.h
@@ -222,6 +222,7 @@
 extern "C" {
 #endif
 
+  int match_multi_entry(const char *key, const char *field, unsigned index);
   int wait_and_unmount(const char *mountpoint, bool kill);
 
   typedef int (*kdf_func)(const char *passwd, const unsigned char *salt,