Closes #1619

Most could use the each method, but because of the hack used to
disambiguate old- and new-style loops, some had to use vec::each.

(This hack will go away soon.)

Issue #1619

Keep their aux builds from stomping on each other

This is not something most people want to be doing and may
be a source of error.

and introduce more indirection where it may be needed

Add len to str extensions

Use node IDs rather than types to ensure exported names are unique.
duplicate symbol. Closes #2074.

In the tutorial, use the crate_type attribute when discussing crate files that
are libraries, and only refer to the --lib files when talking about making a
single source file into a library.

Closes #2070.

Because terr_record_mismatch was getting called by infer::flds,
which takes types a and b where it's trying to prove a <: b, the
expected and actual fields were switched. Fixed it. Closes #2094

This example got left out for some reason.

Closes #2120.

This will be used for stack crawling, which in turn will be used for GC and
unwinding.

- we now distinguish bound/free parameters (see region-param
  test case for why this is necessary)
- we also track bounds on region variables
- also, restructure fold_ty() to have multiple variants without
  duplication instead of one overloaded folder.  This also allows
  for using block functions.

Add an optional --logfile argument to std::test::test_main and to
compiletest.

Use this features and the new 'check-summary.py' script to
summarise all the tests performed by the 'check' target. This is
a short term fix for #2075.