patchbomb: fix From_ in the message's envelope
Localized date in the From_ prevents MUAs like mutt from parsing mbox files
generated by patchbomb. Using a 24 characters date in asctime format instead.
adding a
now at: a.patch
applying b.patch
applying c.patch
now at: c.patch
now at: b.patch
% Using index
now at: a.patch
applying b.patch
applying c.patch
now at: c.patch
% No warnings when using index
now at: b.patch
applying c.patch
applying bug314159
now at: bug314159
% Detect ambiguous non-index
patch name "14" is ambiguous:
bug314159
bug141421
abort: patch 14 not in series