Paver: fail if pylint/pep8 violations threshold is breached.

I would just write this function as:
```python
PYLINT_VIOLATION_RE = re.compile(r"^[C|R|W|E|F]:")

def num_pylint_violations(report_file):
    """
    Assume that all violations have a line that starts with either C, R, W, E, or F,
    followed by a colon. This indicates the severity of the violation: convention,
    refactor, warning, error, or fatal. See the output of `pylint --long-help` for more
    information.
    """
    return sum(1 for line in open(report_file) if PYLINT_VIOLATION_RE.match(line))
```