patchbomb: mime-encode headers and parts not containing patches
Do nothing for "hg email --test" to preserve display.
% qimport non-existing-file
abort: unable to read non-existing-file
% build diff with CRLF
adding b
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% qimport CRLF diff
adding b.diff to series file
applying b.diff
Now at: b.diff