Allow mutable slices in statics.

Fixes #11411
rustc: Move mut slice check to `check_static`

This is a follow-up patch that moves the mut slice check to the recently
added `check_static`

Closes #11411
getopts missing docs
Add method Vec<T>::as_mut_ptr()
Remove AtomicFlag

fixes #12943
Doc-sprint: Document endian conversion functions
`strdup_uniq` doesn't have to be `pub`.
auto merge of #12942 : alan-andrade/rust/docathon-getopts, r=alexcrichton

https://docs.google.com/spreadsheet/ccc?key=0An9tLRVf1SSfdE9jX1Q2QkhiUGVwTnh5YTJnMHVUYXc&usp=sharing#gid=6
auto merge of #12944 : mcpherrinm/rust/master, r=alexcrichton
auto merge of #12945 : cadencemarseille/rust/vec_ng-as_mut_ptr, r=alexcrichton
De-@ Session usage.
De-@ ty::ctxt usage.
De-@ tyencode::ctxt and related parts of astencode.
De-@ liveness.
De-@ type checking contexts.
De-@ trans contexts.
De-@ reachable.
De-@ filesearch.
De-@ CStore uses.
De-@ ParseSess uses.