Add a redo.py script which takes a session directory name as arg and digs into the directory

to find out the tests which failed/errored and need re-running.  The dotest.py test driver
script is modified to allow specifying multiple -f testclass.testmethod in the command line
to accommodate the redo functionality.

An example,

 $ ./redo.py -n 2011-07-29-11_50_14
adding filterspec: TargetAPITestCase.test_find_global_variables_with_dwarf
adding filterspec: DisasmAPITestCase.test_with_dsym
Running ./dotest.py -v  -f TargetAPITestCase.test_find_global_variables_with_dwarf -f DisasmAPITestCase.test_with_dsym

...

----------------------------------------------------------------------
Collected 2 tests

1: test_with_dsym (TestDisasmAPI.DisasmAPITestCase)
   Exercise getting SBAddress objects, disassembly, and SBAddress APIs. ... ok
2: test_find_global_variables_with_dwarf (TestTargetAPI.TargetAPITestCase)
   Exercise SBTarget.FindGlobalVariables() API. ... ok

----------------------------------------------------------------------
Ran 2 tests in 15.328s

OK

llvm-svn: 136533