pull: Fix use-after-free

The strchr() was pointing into a string we were freeing.
fetcher: Close request body on error paths

Otherwise, we're potentially holding up subsequent requests.

I was hitting this when testing the metalink code, where we want to
continue doing more fetches after hitting a 404.

https://bugzilla.gnome.org/show_bug.cgi?id=729585
Bump GIO dependency to 2.38 for GTask

I'd like to use GTask, so bump the dependency.

https://bugzilla.gnome.org/show_bug.cgi?id=729585
Add repository "summary" file and metalink support

For Fedora and potentially other distributions which use globally
distributed mirrors, metalink is a popular solution to redirect
clients to a dynamic set of mirrors.

In order to make metalink work though, it needs *one* file which can
be checksummed.  (Well, potentially we could explode all refs into the
metalink.xml, but that would be a lot more invasive, and a bit weird
as we'd end up checksumming the checksum file).

This commit adds a new command:

$ ostree summary -u

To regenerate the summary file.  Can only be run by one process at a
time.

After that's done, the metalink can be generated based on it, and the
client fetch code will parse and load it.

https://bugzilla.gnome.org/show_bug.cgi?id=729585
Drop g_type_init() call now that we depend on GLib 2.36
doc: Add a man page for summary command
build: Unify CPPFLAGS settings

The libostree core uses SYSCONFDIR now, so we should ensure it's used
consistently.  Someone else was seeing SYSCONFDIR not being defined
while compiling with a newer automake version, which may process
CPPFLAGS more precisely.
build: We also work OK with LZMA 5.0

This is the version that's in Slackware at the moment at least.
pull: Squash some uninitialized variable warnings
Release 2014.6
cherry-pick: Add cherry-pick command, as a simpler commit --tree=ref=...

Add a cherry-pick command, as git does. This mostly works the same way
as --tree=ref= to commit, but if you don't override the subject and
message it'll reuse the values from the original commit.
cherry-pick: Add documentation for cherry-pick command
Move cherry-pick helper functions to builtins-common
Use commit helper functions from builtins-common