Adds conditional byteswapping intrinsics

These intrinsics are synthesized, so maybe they should be in another
file. But since they are just a single line of code each, based on the
bswap intrinsics and aren't really intended for public consumption (they should be exposed as a
single function / trait) I thought they would fit here.
Implement `map_mut` on the Option type

Closes #7394
configure: Require one of wget or curl.
When an impl references an unknown trait, mention what
the trait is called in the error message.
Add an EnumSetIterator and EnumSet::iter
Move most iter functionality to extra, fixes #7343
extra: docs, tests and new functionality for the extra::stats module
Classify newtype structs S(T) as immediates if T is an immediate
lint: make the non_camel_case_types lint work with scripts without a upper/lowercase distinction.
rustc: add a lint to enforce uppercase statics.
Fix dereference of temporary immediate newtype structs
Improve the attempted dynamic environment-capture error message
Better error messages in report_use_of_moved_value; close #7286
Fix filenames of some compile-fail tests.
Add a run-pass test for recursive copyable stack closures.
Defer reasoning about region relationships until after regionck.

This patch makes error handling for region inference failures more
uniform by not reporting *any* region errors until the reigon inference
step. This requires threading through more information about what
caused a region constraint, so that we can still give informative
error messages.

I have only taken partial advantage of this information: when region
inference fails, we still report the same error we always did, despite
the fact that we now know precisely what caused the various constriants
and what the region variable represents, which we did not know before.

This change is required not only to improve error messages but
because the region hierarchy is not in fact fully known until regionck,
because it is not clear where closure bodies fit in (our current
treatment is unsound). Moreover, the relationships between free variables
cannot be fully determined until type inference is otherwise complete.

cc #3238.
Correct handling of if/match, and make explicit computation of
common supertypes.

This was breaking with the change to regions because of the
(now incorrect) assumpton that our inference code makes,
which is that if a <: b succeeds, there is no need to compute
the LUB/GLB.
move docs into doc.rs
convert region_inference into a module, so I can attach docs
Move existing docs into doc.rs