Description of problem:
When several attachments are included in an email, the 'Save All' function is
very useful.  However, if any of the attachment filenames are the same as each
other, not all of the attachments will be saved, i.e. the filenames are trusted
to be unique.

Version-Release number of selected component (if applicable):
evolution-2.10.3-4.fc7

How reproducible:
100%

Steps to Reproduce:
1.Send an email and attach two different images both named 'image.jpg'
2.Using evolution to read the email, click 'Save All' at the top of the message.
  
Actual results:
Only one 'image.jpg' file is saved.

Expected results:
Some unique extension should be added to the end of the filename, in the same
way as when nautilus pastes a file into a directory in which a like-named file
already exists.

Setting severity to high because this can result in unintentional data loss with
no warning.