Update phpunit to 4.x.

Had to add another line to a testcase in order to maintain 100% code
coverage.  4.x seems to fix a code coverage bug that was causing a line
previously uncovered to be reported as covered.
Remove unnecessary arguments to composer install.

We don't set these elsewhere and don't need to set them here.
Fix indentation in phpunit.xml.
Specify test suite in phpunit.xml.
Use PHPUnit as a library.
Restrict codesniffer to 1.4.x.

1.5 was backwards breaking from our standpoint here.  At some point we
need to update it, but that is not a simple change.
Remove --dev from composer install.

--dev is the default.