patchbomb: Support initial in-reply-to header
This allows follow-up/revised patches to appear properly threaded
in mail readers and in the archives, reducing noise.
3 files updated, 0 files merged, 0 files removed, 0 files unresolved
% merge heads
HG_FILE l
HG_MY_ISLINK 1
HG_OTHER_ISLINK 0
HG_BASE_ISLINK 0
merging l
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
% merge working directory
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
HG_FILE l2
HG_MY_ISLINK 1
HG_OTHER_ISLINK 0
HG_BASE_ISLINK 0
merging l2
0 files updated, 1 files merged, 0 files removed, 0 files unresolved