Add missing call to file.path

see https://github.com/hadley/devtools/commit/44c247231622231c6611a7bfa0a4ed2ae5289c95#commitcomment-6867162
Merge pull request #515 from krlmlr/patch-2

Add missing call to file.path
fix three documentation typos

"know" -> "known" and
"must not have an ERRORs" -> "must not have *any* ERRORs"
"it's" -> "its"
load_all: Re-export imported objects. Fixes #518
Add tests for re-exporting imported objects
The R CMD option rebuild vingettes has been renamed build vingettes
Merge pull request #521 from statwonk/master

The R CMD option rebuild vingettes has been renamed build vingettes
Re-document
Re-generate svn docs
Remove unused svn-path.Rd file
document: use namespace env instead of package env
Fix a typo ("all all").
Merge pull request #528 from craigcitro/patch-1

Fix a typo ("all all").
Merge pull request #517 from scottkosty/patch-2

fix three documentation typos
Update cran notes
Re-roxygenise
Re-re-roxygenise
Improve release docs
Remove extra space in doc file name
Remove no-longer-needed get_namespace function