Fixes clang autodescribe to support boolean template arguments and string literal function default arguments

gccxml doesn't like the new tests, but clang seems to pass
```
ERROR: test_autodescribe.test_describe_cpp('gccxml',)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/home/tewk/xdress/tests/test_autodescribe.py", line 181, in check
    clang_includes=clang_includes)
  File "/usr/local/lib/python2.7/dist-packages/xdress-0.4_dev-py2.7.egg/xdress/autodescribe.py", line 2087, in describe
    clang_includes=clang_includes)
  File "/usr/local/lib/python2.7/dist-packages/xdress-0.4_dev-py2.7.egg/xdress/autodescribe.py", line 382, in gccxml_describe
    describer = describers[kind](name, root, onlyin=onlyin, ts=ts, verbose=verbose)
  File "/usr/local/lib/python2.7/dist-packages/xdress-0.4_dev-py2.7.egg/xdress/autodescribe.py", line 825, in __init__
    self.desc['type'] = ts.canon(name)
  File "/usr/local/lib/python2.7/dist-packages/xdress-0.4_dev-py2.7.egg/xdress/utils.py", line 705, in __call__
    cache[key] = self.meth(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/xdress-0.4_dev-py2.7.egg/xdress/typesystem.py", line 1438, in canon
    return (self.canon(t0), last_val)
  File "/usr/local/lib/python2.7/dist-packages/xdress-0.4_dev-py2.7.egg/xdress/utils.py", line 705, in __call__
    cache[key] = self.meth(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/xdress-0.4_dev-py2.7.egg/xdress/typesystem.py", line 1399, in canon
    _raise_type_error(t)
  File "/usr/local/lib/python2.7/dist-packages/xdress-0.4_dev-py2.7.egg/xdress/typesystem.py", line 3161, in _raise_type_error
    raise TypeError("type of {0!r} could not be determined".format(t))
TypeError: type of 'Point' could not be determined

----------------------------------------------------------------------
Ran 393 tests in 29.919s
```