convert/gnuarch: parse continuation-of revisions in gnuarch source In GNU Arch, continuation-of was often used for: - tagging revisions - continue working on a project in a new archive, because arch was scaling poorly in revision numbers (cat-logs were slow to be parsed and scanned through) - very similar to the previous point, fork his own branch of a project. Parsing this header information will allow to 'follow' new history because it often hints at older/forked/personal revision trees. This patch however just implements the parsing of the continuation-of header. A followup patch will implement the proper use of this new information.

% add file
adding qqq.txt
% commit first revision
% set bookmark
% commit second revision
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% update to -2
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% commit new head
created new head
% bookmarks updated?
   test                      1:16b24da7e457
   test2                     1:16b24da7e457
% strip to revision 1
saving bundle to 
saving bundle to 
adding branch
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
% list bookmarks
 * test                      1:9f1b7e78eff8
 * test2                     1:9f1b7e78eff8