Use warn+heap when running 'make test'

[Dan Kegel]

As noted in http://bugs.winehq.org/show_bug.cgi?id=9916
using warn+heap poisons free memory, and finds a few
more bugs.

People who run 'make test' should consider running
 WINEDEBUG=warn+heap make test
instead.

(I don't know whether we should make that the default, though.
Anyone have an opinion?)