runtime/race: say where the memory block was allocated

[dvyukov]

C++ ThreadSanitizer describes where the memory involved in report was allocated:
http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/tsan/lit_tests/malloc_stack.cc?revision=187875&;view=markup

It would be useful to do the same for Go.

C++ ThreadSanitizer can also pronounce the name of the global (if the race in on
global). Look if it's possible in Go.

[rsc]

Comment 1:

Labels changed: added go1.3maybe.

[rsc]

Comment 2:

Labels changed: added release-none, removed go1.3maybe.

[rsc]

Comment 3:

Labels changed: added repo-main.

[gopherbot]

CL https://golang.org/cl/19958 mentions this issue.