auto merge of #6734 : huonw/rust/gitignore, r=thestinger

Author: bors

.gitignore

@@ -73,6 +73,7 @@ src/.DS_Store
 /doc/html
 /doc/latex
 /doc/std
+/doc/extra
 /nd/
 /llvm/
 version.md
@@ -81,7 +82,6 @@ keywords.md
 x86_64-apple-darwin/
 x86_64-unknown-linux-gnu/
 i686-unknown-linux-gnu/
-doc/core/
 tmp.*.rs
 config.stamp
 .DS_Store