Infinite recursion error when debugging TaurusValueSpinBox

While debugging #707 (closed) we hit a strange recursion error if we try to put a print in TaurusValueSpinBox.validate()

The problem can be reproduced with the following snippet:

from taurus.qt.qtgui.application import TaurusApplication
from taurus.qt.qtgui.input import TaurusValueSpinBox
from taurus.external.qt import Qt
import taurus

class A(TaurusValueSpinBox):
    def validate(self, input, pos):
        val = self.lineEdit().validator()
        taurus.debug('asd')
        if val is None:
            return Qt.QAbstractSpinBox.validate(self, input, pos)
        return val.validate(input, pos)

app = TaurusApplication()
w = A()
model = 'sys/tg_test/1/double_scalar'
w.setModel(model)

When running it, I get:

Traceback (most recent call last):
  File "/home/cpascual/.PyCharmCE2017.2/config/scratches/scratch_68.py", line 11, in validate
    taurus.debug('asd')
  File "/home/cpascual/src/taurus/lib/taurus/core/util/log.py", line 1019, in debug
    return __getrootlogger().debug(msg, *args, **kw)
  File "/home/cpascual/src/taurus/lib/taurus/core/util/log.py", line 1004, in __getrootlogger
    return Logger.getLogger("TaurusRootLogger")
  File "/home/cpascual/src/taurus/lib/taurus/core/util/log.py", line 656, in getLogger
    cls.initRoot()
  File "/home/cpascual/src/taurus/lib/taurus/core/util/log.py", line 526, in initRoot
    return cls._getLogger()
  File "/home/cpascual/src/taurus/lib/taurus/core/util/log.py", line 652, in _getLogger
    logging.setLoggerClass(orig_logger_class)
  File "/usr/lib/python2.7/logging/__init__.py", line 996, in setLoggerClass
    if klass != Logger:
RuntimeError: maximum recursion depth exceeded in cmp
(...) (REPEATED SEVERAL TIMES)

By using git bisect, the problem seems to be starting with 69c39a61 and, indeed, if we comment out the call to setValue in the first if block of TaurusValueLineEdit.handleEvent() (which was introduced with 69c39a61) this problem is gone.