rdar://problem/9173060 lldb hangs while running unique-types

disappears if running with clang version >= 3.  Modify the TestUniqueTypes.py
to detect if we are running with clang version < 3 and, if true, skip the test.

Update the lldbtest.system() function to return a tuple of (stdoutdata, stderrdata)
since we need the stderr data from "clang -v" command.  Modify existing clients of
lldbtest.system() to now use, for example:

         # First, capture the golden output emitted by the oracle, i.e., the
         # series of printf statements.
-        go = system("./a.out", sender=self)
+        go = system("./a.out", sender=self)[0]
         # This golden list contains a list of (variable, value) pairs extracted
         # from the golden output.
         gl = []

And add two utility functions to lldbutil.py.

llvm-svn: 128162