Bug 495337 - Make sessionStorage use principals instead of string domains, r=bz+bclary

caps/idl/nsIPrincipal.idl

caps/src/nsNullPrincipal.cpp

caps/src/nsPrincipal.cpp

caps/src/nsSystemPrincipal.cpp

docshell/base/nsDocShell.cpp

dom/src/storage/nsDOMStorage.cpp

...hitest/sessionstorage/test_sessionStorageFromChrome.xhtml

js/src/tests/ecma/ExecutionContexts/jstests.list

js/src/tests/ecma_2/Statements/jstests.list

js/src/tests/js1_5/Array/jstests.list

js/src/tests/js1_6/extensions/jstests.list

js/src/tests/js1_7/extensions/jstests.list

js/src/tests/js1_8/extensions/jstests.list