Description of problem:
Evolution won't save an account's default signature as 'None' if it
has ever been changed from 'None' and saved. Confused yet? The steps
to reproduce should help explain... if not, come yell at me ;)

Version-Release number of selected component (if applicable):
evolution-1.5.94.1-1

How reproducible:
Always

Steps to Reproduce:
1. On an account that has never had a default signature other than 'None':
2. Select a real signature, such as 'Autogenerated' or a custom sig
3. Press OK
4. Re-enter that account's Properties dialog
5. Select signature 'None'
6. Press OK
  
Actual results:
Default signature remains what was selected in step 2.

Expected results:
Default signature is 'None'.