pullrequests: refactor PullRequestModel().create The database lookups of the user and repositories are moved outside, into the callers, which have already looked up the relevant objects, thus saving two database lookups when creating a PR.

[tox]
minversion = 1.8
envlist = py{26,27}-pytest

[testenv]
setenv =
    PYTHONHASHSEED = 0
deps =
    -r{toxinidir}/dev_requirements.txt
    py26-pytest: unittest2
    python-ldap
    python-pam
commands =
    pytest: py.test {posargs}