Expand non replacement check to bool types

We also need to avoid trying to parse bool types when not replacing as
they may be unsubstituted variables that are not a valid bool type. Just
don't check them if we are not replacing and use the default value
instead.

Author: cboylan

tests/test_config.py

@@ -352,6 +352,7 @@ def test_reproduce_issue595(self, newconfig):
             setenv = DONTCARE = 0
             [testenv:eggs]
             setenv = {[testenv]setenv}
+            sitepackages = {[testenv]sitepackages}
         """)
         assert config.envlist == ['spam']
 

tox/config.py

@@ -980,7 +980,7 @@ def _getdict(self, value, default, sep, replace=True):
 
     def getbool(self, name, default=None, replace=True):
         s = self.getstring(name, default, replace=replace)
-        if not s:
+        if not s or not replace:
             s = default
         if s is None:
             raise KeyError("no config value [%s] %s found" % (