malloc_conf does not reliably work with MSVC, which complains of
"inconsistent dll linkage", i.e. its inability to support the
application overriding malloc_conf when dynamically linking/loading.
Work around this limitation by adding test harness support for per test
shell script sourcing, and converting all tests to use MALLOC_CONF
instead of malloc_conf.
Fix a regression in prof_dump_ctx() due to an uninitized variable. This
was caused by revision 4f37ef693e3d5903ce07dc0b61c0da320b35e3d9, so no
releases are affected.
