refspec: add direction accessor
remote: add resfpec list accessors

Bring back a way of acessing the git_refspec* from a remote.

Closes #1514
remote: fix a leak when dwim'ing refspecs
Catch issue in config set with no config file

This prevents a segfault when setting a value in the config of a
repository that doesn't have a config file.
Merge pull request #1522 from arrbee/repo-open-with-no-config

Catch issue in config set with no config file
Merge pull request #1520 from carlosmn/nth-refspec

Add refspec list accessors