add MAIL_ASCII_ATTACHMENTS, to force ascii filenames for attachments
document MAIL_ASCII_ATTACHMENTS
fix for python 2.6 support
py2.6 compat: number placeholders in string.format
ascii_attachments: don't process filename's extension apart
more doc about MAIL_ASCII_ATTACHMENTS
Merge pull request #84 from bmathieu33/ascii_filenames

Ascii filenames