getSourceForPkgRecord installs from GitHub via SHA1 and not via file name
download .tar.gz file
fix expressionDependencies on expression


 - The value from recursive calls should be returned
 - `fileDependencies` always call `expressionDependencies` with language or symbols instead of            expression, so this chunk is never used and can be safely removed for now.
don't write lock file until snapshot is complete to avoid inconsistency between sources and lock file
collect errors while getting sources for multiple packages, output all errors at the end
remove unused
fetch repository URLs from packrat.lock
bugfix
also fetch sources for dependencies

regression introduced in 6e1790fd9d934f
refactor: extract variable appPackagesFlat
Merge branch 'travis' into bootstrap
need sourcePath
Merge pull request #39 from krlmlr/in-dir-tar

replace broken on.exit with in_dir when calling tar
Add Travis to README
Merge pull request #40 from krlmlr/install-github-sha1

Install packages from GitHub via SHA1 and not via named reference
Merge pull request #44 from luckyrandom/patch-1

fix expressionDependencies on expression
Merge pull request #45 from krlmlr/bootstrap

Streamline bootstrapping
Strip whitespace; update .Rproj settings; re-roxygenize
Import pkgVignettes from tools
Only re-set CYGWIN if it's already set