def-id we have, so that the inliner can distinguish between external and
internal def-ids.  Also add some comments explaining the distinction!

Fixes #4516.

r=graydon

Revert "librustc: Make unqualified identifier searches terminate at the nearest module scope. r=tjc"

This reverts commit a8d37af2.

~20% perf win for trans on -O0, with other minor improvements across the board.
No effect on -O2.

librustc: Encode language items into a special lookup table. 9% improvement in hello world compile time.

librustc: Terminate name searches at the nearest module scope for paths that contain at least two components. r=graydon

and rename "class" to "struct" everywhere possible (except local
vars, I was too lazy for that) -- that is why this commit is so
big.

No review, just dead code removal and renaming.

Closes #3515

Closes #4076

If an enum type's only variant is private, disallow dereferencing
values of its type.

Due to #4082, this only applies to enums that are in the same crate.

r=pcwalton

Closes #818

Minor refactoring, no review.

Closes #2739

This is minor and probably completely inconsequential to performance,
but I find vec::map to be more clear than vec::each and a push.

of the 0th.  0th is only correct when there are no bound tps
on the trait.

Fixes #3741.

This commit replaces nearly all remaining uses of #fmt, #debug, #error,
and #info, and fixes some error messages...

This reverts commit ed3689d5.