git-svn: Add per-svn-remote ignore-paths config

git-svn: Add per-svn-remote ignore-paths config

The --ignore-paths option to fetch is very useful for working on a subset
of a SVN repository.  For proper operation, every command that causes a
fetch (explicit or implied) must include a matching --ignore-paths option.

This patch adds a persistent svn-remote.$repo_id.ignore-paths config by
promoting Fetcher::is_path_ignored to a member function and initializing
$self->{ignore_regex} in Fetcher::new.  Command line --ignore-paths is
still recognized and acts in addition to the config value.

Signed-off-by: Ben Jackson <ben@ben.com>
Acked-by: Eric Wong <normalperson@yhbt.net>