Make autoCompilerPlugins support compiler plugins defined in a internal dependency

requires the compiler plugin project to define exportJars := true
make ScopeFilter accessible without a qualifier

Should be improved: ideally there would only be a single top-level alias.
Deprecate old Scala+Java fork interfaces in favor of Fork+ForkOptions
don't put Scala jars on forked boot classpath by default

Ideally, Scala jars on the normal classpath would be moved to the boot classpath,
but this is more involved.
Fork run directly with 'java' to avoid additional class loader from 'scala' command.  Fixes #702.
Undeprecate ScalaInstance.libraryJar, which will be reliable for modularized Scala.
Docs: Fixed name of http_proxy env var
Docs: fix formatting in LocalScala from initial conversion to rST
Docs: move contents of dormant configurations page into Library-Management
fix scripted tests
remove resident compiler code

The infrastructure for resident compilation still exists,
but the actual scalac-side code that was backported is removed.
Future work on using a resident scalac will use that invalidation
code directly from scalac anyway.
drop canonicalization of files on classpath and other cleanup.  Fixes #723.
remove long obsolete sbt_pending directory left over from 0.7 conversion
memoize .sbt file loading within a build and only add a Project once

This fixes an infinite loop when defining a Project in a .sbt file
with the build base directory as the project base directory.
This allows the standard behavior for interpreting settings from
.sbt files for both Projects defined in .sbt files as well as in
.scala files. That is, settings in .sbt files in "." go in all
projects with "." as their base directory.

Ref #554.
Use a default root project aggregating all projects if no root is defined.  Fixes #697.

Ref #554.
Better auto-generated IDs for default projects.  Fixes #554.

For the global plugins project, the default ID is "global-plugins".
For a normal project, the default ID is the name of the build directory.
The ID of a build definition for one of the above appends -build.
work around URI problems with encoding and resolving. Fixes #725
Test for #723.
Allow -cp argument to 'apply' command to be quoted.  Fixes #724.
Add xsbt-coveralls-plugin to list of code coverage plugins