Refactor core::run to remove the ProgRepr struct, which was
a legacy from the time when destructors were implemented
using resource types.
Removed ascii functions from other modules

Replaced str::to_lowercase and str::to_uppercase
Fixed typo... And a billion other things.
auto merge of #6029 : Kimundi/rust/ascii-encoding, r=thestinger

Replaced {str, char, u8}::is_ascii
Replaced str::to_lower and str::to_upper
auto merge of #6044 : Dretch/rust/run-remove-progrepr, r=graydon

...which was a legacy from the time when destructors were implemented using resource types.
core: Comments only -- move FIXME to correct location
rustpkg: update README saying which tests pass
rustpkg: Make path searching work as described in the rustpkg doc

rustpkg now searches for package directories in ./src rather than
in . . I also added a rudimentary RUST_PATH that's currently
hard-wired to the current directory. rustpkg now uses src/, lib/,
and build/ directories as described in the manual.

Most of the existing test scenarios build now; the README file
(in a separate commit) explains which ones.
rustpkg: Correct directory structure in test scenarios
rustpkg: Preliminary work on install command

Mostly just tests (that are ignored); install command is still
stubbed out.