un-deprecrate
Merge pull request #508 from krlmlr/patch-1

un-deprecrate
remove branch parameter to install_github
Deprecate and remove pull parameter to install_github

- New exported function github_pull() to be used as value for ref parameter
- Implemented using a simple S3 dispatch mechanism
- Tests with improved mocking
    - new function with_mock
- Tests for warning when using deprecated parameters branch and pull
update NEWS
Add 'install_svn' functions
Fix 'install_svn' man pages
Merge pull request #510 from julian-gehring/install-svn

Add 'install_svn' functions
Add missing httr pieces
Use new cran comments naming scheme
don't use with(), fix indentation
clean up
refactor: inline function, rename variables; this affects an existing test
document S3 generic
rename class pull to github_pull, inline function github_pull_info
Merge pull request #509 from krlmlr/509-install_github-s3-ref

Clean up install_github parameters pull and branch
Prompt to install build tools when needed.
Closes #488
allow installing the latest GitHub release by passing ref = github_release(), or using the syntax "user/repo@*" in install_github

- update NEWS
- supply test
- host for GitHub API is specified only once in the code