Removed fake dependecies on .gct

These were frocing the gcts to be bult before the compiler.
Modifies Makefile and some tests.

In Makefile, clarifies role of $(KG), l1 and l2 directories.
Moves compilations out of receipies and into dependencies
so that they are executed only when required.

Adds stubs dom.grace for the Web DOM, and imports.grace
for the mysterious "imports" module.
Updates configure to define STUBS.

Changes lookup-path logic for imports.
Modules genc and genjs now use the same path lookup
as identifierresolution.  TODO: move all of these
lookups into identifierresolution and use the same method
for all three; checkImports should happen when the .gct
is accessed.

Modifies logic used to locate gracelib.o when linking.

Moves all 2(!) regression tests into tests directory and
made them run.  Made test for the requireTypes module run
without installation.  Changes names of dialects in *Example
programs to match their actual names.

Makes target tests depend on minigrace-environment, rather
than minigrace. Removes prerequisites with { … }, since
they didn’t work with recursive make.
Updates comments.

Specifies the dependencies of the unicodegen tool in
a comment.
Uses relative path to requireTypes.

This makes it possible to run tests on rtObjectdraw
without installing requireTypes

Changes source of  t161_requireTypes so that it finds
the requireTypes dialect.
Patches gracelib.c to use just the basename of the
module pathname when constructing the name of the
module’s init function.