[plt-scheme] 301.13

MzScheme and MrEd are now version 301.13 in the SVN repository trunk.

This version continues a series of changes that will result in simpler
installers on Mac OS X and Windows, more flexibility in re-packaging
PLT Scheme for Unix variants, and better support for creating your own
stand-alone executables.

One effect of the changes is that the concept of "PLTHOME" is going
away. Instead of a root directory that contains all other parts of a
PLT installation, there will be functions to find the main "collects"
directory, the "lib" directory, etc., and the locations of those
directories will be configurable. Those functions are not ready, yet.

Starting with 301.13, however, MzScheme and MrEd no longer recognize
the PLTHOME environment variable. The (relative) path to the main
"collects" directory is embedded in each executable. Eventually, paths
to other directories (such as "lib") will be embedded in a "config"
collection.

Meanwhile, for Unix and Mac OS X, a launcher script refers to an
executable through a path that's relative to the script itself.
Combined with the recent changes for Mac OS X to support frameworks
relative to the executable, this means that the Mac OS X distribution
can be drag-and-drop, instead of an installer.

Finally, when creating a stand-alone executable, the path to "collects"
within the executable can be set (e.g., with mzc's new `--collects'
flag). This makes it easier to distribute extra files that are needed
by the executable. Soon, we'll add tools for putting a copy of shared
libraries with a set of generated executables, so that the resulting
package is truly "stand-alone".

Matthew