rename t to tau
stop doing slow computation whose results were useless

also, clean up drawing of 'insert large letters' dialog
so that you don't see a little white sliver when there are
no characters typed
fix r6rs link just link in 8d3fd26c6
fix rule reference in tutoral, also spell-check

closes PR 14676
fix run-time error reporting for variables in a submodule

Error reports used the "source" field of a module, which
doesn't have submodule information, or the "name" field of
a module, which might not match an actual filename (".ss"
vs. ".rkt"). Create the right combination.
fix `rename-transformer-target` for chaperoned structs
fix "props" for "pict-snip-pkgs"
meta/new-web: use `--web` mode of `raco s3-sync`

A side effect of this change is that ".html" files bigger than
1k are gzipped, in addition to ".css" and ".js" files. I find
several web comments to the effect that gziping ".html" files works
fine, because all browsers support it, and no warnings against.
Since gzipping ".css" and ".js" files has worked fine for us, too,
lets take the plunge and try gzipping ".html".
web pages: update news to v6.1
avoid cross-namespace submodule pollution via module-code cache

When a module is loaded with submodules intact, it should not be
cached and used for a later load that is intended to obtain the
module without submodules. Avoid mismatches by constraining the
cache to modules without submodules.
racket/place: protect place-creation bindings

Closes PR 14677
Change RacketCon talk title.
SenoraGC: support allocation of executable memory; tune for performance

Allocation of executable memory is intended to make SELinux
happier by mmapping with PROT_EXEC instead of using mprotect()
to allow execution after the fact.

Performance improvements bring SGC within 30% of the Boehm GC on
`racketcgc -cl racket`, which makes SGC an even more plausible
substitute.
racketcgc: use SenoraGC instead of Boehm GC by default

This new default for Unix and Mac OS X trades performance for
portability (hopefully), but for most users the switch affects only
for the build process, where `racketcgc` is used to build `racket`.

To continue using Boehm GC, configure with `--disable-sgc`.

For now, Boehm GC continues to be the default for Windows.
windows: switch projects to SGC by default
windows: fix sgc allocation of executable pages
avoid NULL argument to memcpy()

gcc 4.9 takes advantage of the specification of undefined behavior if
you pass a NULL to memcpy(), even if the last argument is 0
remove accidentally added file
windows: remove custom manifest

The manifest was intended to enable XP-style controls, but at this
point it doesn't seem to do anything except interefere with some
variants of the build tools.
Windows: more changes to auto-adapt to Visual Studio version

Although newer versions of Visual Studio can open 2010 projects, the
meaning of the project turns out to be: use 2010 tools. So, I've added
a step in the build script to automatically upgrade the solutions and
projects based on the version of Visual Studio that is being run.

Meanwhile, since my previous tests for VS 2012 and VS 2013 were using
VS 2010 projects, I wasn't actually testing with the 2012 and 2013
compilers. Additional changes are needed to make those work, notably a
fresh implementation of setjmp() and longjmp() for Win64.

This was all very painful, but the projects are now in much better
shape, so maybe it won't be so bad from here.