Enable SIGABRT handler on desktop OS X

The iOS port has a SIGABRT handler which turns out to be useful on desktop OS X
for a number of reasons (https://bugzilla.mozilla.org/show_bug.cgi?id=717758,
for example). The code as-written mostly works, it just needed the extra
handling in MinidumpGenerator::GetThreadState to do the right thing. I spent
extra time writing the unit test because without that block of code it still
produced minidumps, but the exception context was all wrong. I still can't
figure out how to write a really rigorous unit test, but I gave up.

[Ted Mielczarek]

Sorry, I was having build issues on 10.8 and resorted to hacking the XCode
projects, didn't mean to include those in the diff.

[Mark Mentovai]

LGTM

https://breakpad.appspot.com/618002/diff/3001/src/client/mac/tests/exception_...
File src/client/mac/tests/exception_handler_test.cc (right):

https://breakpad.appspot.com/618002/diff/3001/src/client/mac/tests/exception_...
src/client/mac/tests/exception_handler_test.cc:140: }
…otherwise expect that it’s not this pair?

https://breakpad.appspot.com/618002/diff/3001/src/client/mac/tests/exception_...
src/client/mac/tests/exception_handler_test.cc:148: // Ideally would like to
sanity check that abort() is on the stack but that's hard.
80

https://breakpad.appspot.com/618002/diff/3001/src/client/mac/tests/exception_...
src/client/mac/tests/exception_handler_test.cc:152:
memory_list->GetMemoryRegionForAddress(instruction_pointer);
Continuation lines are +4, not +2.

[Ted Mielczarek]

Committed:
http://code.google.com/p/google-breakpad/source/detail?r=1205