Constant-time utilities

Pull constant-time methods out to a separate header, add tests.

Reviewed-by: Bodo Moeller <bodo@openssl.org>
diff --git a/crypto/Makefile b/crypto/Makefile
index 0537913..8744957 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -31,6 +31,7 @@
 LIBS=
 
 GENERAL=Makefile README crypto-lib.com install.com
+TEST=constant_time_test.c
 
 LIB= $(TOP)/libcrypto.a
 SHARED_LIB= libcrypto$(SHLIB_EXT)