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.

Ancestors of 5
4 2 0 
Ancestors of 6 and 5
3 4 2 1 0 
Ancestors of 5 and 4
4 2 0 

Descendants of 5
7 8 
Descendants of 5 and 3
6 7 8 
Descendants of 5 and 4
5 7 8