repo: (cleanup) Use _is_system() rather than inlining it

No reason to duplicate the code.
Add more flexible _remote_change() API , expose via 'ostree remote'

For Anaconda, I needed OSTREE_REPO_REMOTE_CHANGE_ADD_IF_NOT_EXISTS,
with the GFile *sysroot argument to avoid ugly hacks.  We want to
write the content provided via "ostreesetup" as a remote to the target
chroot only in the case where it isn't provided as part of the tree
content itself.

This is also potentially useful in idempotent systems management tools
like Ansible.

https://bugzilla.gnome.org/show_bug.cgi?id=741577
tests: Fix two bugs in tests revealed by new remote changes
basic-test: Fixup mtime check for bare-user

https://bugzilla.gnome.org/show_bug.cgi?id=741662
Release 2014.13
Add ostree_repo_remote_list()

Lists available remote names.
Add "ostree remote list" command

Lists available remote names.
doc: Update gtk-docs
Revert "ostree-repo-pull: Remove currently #if 0 static delta code"

This reverts commit 1c2e20af25b21abc0dee1547a0d5bad1a21c0b58.
Static deltas support

https://bugzilla.gnome.org/show_bug.cgi?id=721799
test-rollsum: Process all input, print more statistics

Copying the bup code, we need to loop over all chunks even after
hitting the rollsum returning 0.

Also print more statistics.
fix --help for static-delta

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
Remove unused variable warning