#1 mutt requires attach header filenames to be escaped

[Philip J. Hollenback]

Originally submitted to me dby email by Joost Kremers, adding here so someone eventually incorporates:

When attaching a file with the pseudo Attach: header, mutt requires spaces in filenames to be escaped with backslashes. (At
least, the latest development version, 1.5.20, does.) Post-mode doesn't add them, resulting in an error from mutt.

[Philip J. Hollenback]

patch to escape attach header filenames with spaces.