Fixing the -f option so that one specify multiple filters, e.g.

Fixing the -f option so that one specify multiple filters, e.g.

./dotest.py  -C clang --arch x86_64 --arch i386  -v -t -f ObjCDataFormatterTestCase.test_appkit_with_dsym_and_run_command -f ObjCDataFormatterTestCase.test_appkit_with_dwarf_and_run_command -f TestObjCBuiltinTypes.test_with_dsym_and_python_api -f TestObjCBuiltinTypes.test_with_dwarf_and_python_api -f ObjCDataFormatterTestCase.test_appkit_with_dsym_and_run_command -f ObjCDataFormatterTestCase.test_appkit_with_dwarf_and_run_command -f TestObjCBuiltinTypes.test_with_dsym_and_python_api -f -TestObjCBuiltinTypes.test_with_dwarf_and_python_api

The previous implementation would only remember the last filter passed, and consequently break redo.py

llvm-svn: 170163