Add test for loading files not on filesystem

The new test demonstrates that currently when
a file exists at an older changeset, but not
on the current HEAD, the file is unable to
load.
Add assert to verify initial condition of missing file
Improve missing file test to verify contents of file
Only add file on stream_close() when repo is dirty

Fixes #17
Fix abuse of end() to pass a variable
Merge pull request #17 from donoftime/load-when-not-on-filesystem

Unable to load files not on filesystem at current HEAD
Add tests for listing non existent directories

There are tests both for directories which do not
exist at all, and for directories which do not
exist on HEAD.
Use repo root for cwd to accomodate missing dirs

A bug listDirectory() caused the contents of the
repository root to be returned in the instance
that the specified directory did not exist.

This change leverages the git ls-tree option
"--full-name" to enable the repo root to be used
as the cwd of the process, and the required dir
specified in the ls-tree command itself.
Merge pull request #18 from donoftime/list-non-existent-directories

Listing of non existent directories
updated dependencies (added phpunit 3.7.* because PHPStorm 7 cannot run phpunit 4.*)
updated travis-ci config to use hhvm nightly