Add additional NSDecimalNumber tests

Note that :2155-2157 may not be valid tests; the documentation is contradictory. However they do pass in the simulator.
test for issue #683
Merge branch 'master' of github.com:apportable/FoundationTests
More NSData tests (prep for some really gnarly ones)
test NSDictionary isEqualToDictionary using plist data
offline mode test for nsurlconnection
Merge commit 'apportable/master'
KVO tests of observing dependent key value changing