Makefile: Replace "-fsanitize=address" with "-fsanitize=leak"
The Address Sanitizer is a debugging feature, not a security feature - it has security issues: <http://seclists.org/oss-sec/2016/q1/363> Therefore, it should only be used when debugging. Replace it with "-fsanitize=leak", which is needed since -fsanitize=address no longer includes it implicitly.
* Makefile (DEBUG): Add "-fsanitize=address". (ALL_SANITIZE_OPTIONS): Replace "-fsanitize=address" with "-fsanitize=leak".