Fix a couple of bugs.
* svn-merge2git.sh (extract_svn_branch_name): Properly set
$svn_branch_name to the empty string when we can't figure out the
name of the branch being merged. Also enhance the function to match
some other common patterns found in merge commits.
(find_merge_parent): Strengthen a couple of assertions.
(handling of $opt_remote): When creating a local branch from a
remote branch, schedule it so that it's processed by the main loop.
Signed-off-by: Benoit Sigoure <tsuna@lrde.epita.fr>