'drd', but you may use any tool recognized by your valgrind
installation.
+ As a special case, <tool> can be 'memcheck-fast', which uses
+ memcheck but disables --track-origins. Use this if you are
+ running tests in bulk, to see if there are _any_ memory
+ issues.
+
Note that memcheck is run with the option --leak-check=no,
as the git process is short-lived and some errors are not
interesting. In order to run a single command under the same