Make force parameter work for export operation

The default is changed from 'yes' to 'no' to follow
subversion behavior (ie, requiring explicit confirmation
to erase a existing repository). Since that was not working before
cf #370 and since the option was ignored before and unused, this
should be safe to change.

source_control/subversion.py

@@ -123,7 +123,12 @@ class Subversion(object):
 		
     def export(self, force=False):
         '''Export svn repo to directory'''
-        self._exec(["export", "-r", self.revision, self.repo, self.dest])
+        cmd = ["export"]
+        if force:
+            cmd.append("--force")
+        cmd.extend(["-r", self.revision, self.repo, self.dest])
+
+        self._exec(cmd)
 
     def switch(self):
         '''Change working directory's repo.'''
@@ -173,7 +178,7 @@ def main():
             dest=dict(required=True),
             repo=dict(required=True, aliases=['name', 'repository']),
             revision=dict(default='HEAD', aliases=['rev', 'version']),
-            force=dict(default='yes', type='bool'),
+            force=dict(default='no', type='bool'),
             username=dict(required=False),
             password=dict(required=False),
             executable=dict(default=None),
@@ -202,7 +207,7 @@ def main():
         if not export:
             svn.checkout()
         else:
-            svn.export()
+            svn.export(force=force)
     elif os.path.exists("%s/.svn" % (dest, )):
         # Order matters. Need to get local mods before switch to avoid false
         # positives. Need to switch before revert to ensure we are reverting to