Rename core::private to core::unstable. #4743
Avoid calling to_vec() unnecessarily in parser.

Also, rename the OptVec-to-vector conversion method to
opt_vec::take_vec() and convert from a method into a fn
because I fear strange bugs.
Register FreeBSD snapshot
Merge remote branch 'nmatsakis/parser-perf-problem' into incoming
auto merge of #5190 : brson/rust/snap, r=brson
auto merge of #5165 : brson/rust/unstable, r=brson

r?

This probably isn't controversial, but I want somebody else to sign off on it.
librustc: Forbid chained imports and fix the logic for one-level renaming imports
librustc: Remove `fn@`, `fn~`, and `fn&` from librustc. rs=defun
libsyntax: Remove `fn@`, `fn~`, and `fn&` from libsyntax. rs=defun
libstd: Remove `fn@`, `fn~`, and `fn&` from libstd. rs=defun
libcore: Remove `fn@`, `fn~`, and `fn&` from libcore. rs=defun
test: Remove `fn@`, `fn~`, and `fn&` from the test suite. rs=defun
librustdoc: Remove `fn@`, `fn~`, and `fn&` from compiletest, fuzzer, rustdoc, and rt. rs=defun
librustc: Stop parsing `fn@`, `fn~`, and `fn&`