[backend] Mitigate libgit2 security (umask) issues.
[lib] Update libgit2.
[backend] Make prctl actually work.
Merge branch 'master' of https://github.com/cs136/seashell
Implemented logout button
Made file uploader check if file already exists
Default 'ctdalek' template no longer loaded

Now, instead of the template with foo.c, bar.c, and the ctdalek userid being
loaded before content is replaced by js, a blank screen appears until js
replaces it. If this never happens (i.e., cannot connect to seashell server),
the screen remains blank to avoid confusion.
Removed initial warning dialog
Fixed creds bug

Added a UDP listener that responds to ping. This is used to verify that the
server specified by the given creds file is still running.
[backend] Lock credentials file during read to prevent race conditions.
[backend] Actually use port.
[backend] Read failure handler credentials.
[backend] FFI adjustments.
[backend] Exclusive locks.
[git] Updated libgit2 to current development head.
Merge branch 'master' into directories

Conflicts:
	src/frontend/js/model/project.js