raco pkg update: fix reoprting for `--all` in a scope without packages
raco pkg: fix tests for change `raco pkg show` output
raco pkg update: change printout to avoid alarming "Removing..."

Changed "Removing" to "Uninstalling to prepare re-install of".
Increase SCHEME_PRIM_OPT_TYPE_SHIFT

Otherwise, two optimization flags collide:

 SCHEME_PRIM_ALWAYS_ESCAPES = SCHEME_PRIM_PRODUCES_FLONUM = 8192
Mark immutable? as omitable
fix native-stack caching with libunwind

The implementation of caching stack-trace information in the
stack didn't work right in libunwind mode, with the result that
`(current-continuatiom-marks)` took O(N) time for a continuation
of size N, when it should be amortized constant time.
avoid a compiler warning
Rename racket-extra-test to racket-test-extra.
Split the core racket tests into the "racket-test-core" pkg.

This supports running the core tests on systems which can't run
or don't want to install all the dependencies of the "racket-test"
package.

The "racket-test-core" pkg stil depends on "sandbox-lib" because
the sandbox tests live with the core tests. Hopefully I'll be able
to fix that eventually.
Add configuration for AppVeyor, a Windows CI service.

This configuration will build and test the core of Racket on every
commit. The time constraints are such that only a small portion of
Racket can be built and tested.
Rename to avoid conflict since pkgs is slow.
Use `racket` instead of `scheme`. Fixes dependency issues.
Ignore files here too.
Remove unwanted dependency on mzscheme.

The '#%kernel prop:procedure is the same binding as the mzscheme one.
raco pkg clone: avoid fetching by commit id

A commit id apparently doesn't work in place of a <refexp> in some
versions of Git.
repair a test

The test tried to detect separate evaluations by using the
result of `(current-inexact-milliseconds)`, but a clock's
resolution might not be high enough. Use `(gensym)`, instead.
raco pkg update: better handling of a missing dependency

When updating a linked package whose dependencies have changed,
and when a dependency is missing, then effectively reinstall
the link to get updates as requested by the user.
raco pkg: default `--deps` to `search-ask` in interactive mode

The implemented default for `raco pkg update` actually depended on the
way that a package is installed, and it's difficult to reason about or
to implement the default that is suggested by the documentation.
Meanwhile, `search-ask` seems the most sensible always in interactive
mode (now that we have a way to specify batch mode).
more repairs to stack trace and caching

Fixes problems with d15fda9d6b, but also fixes a problem that
could show up in non-libunwind mode and cause lost frames.
Reduce and fix dependencies for "racket-core-test".

Eventually I'd like to reduce the dependencies further, but this
is enough for now.