SI-4270 Rename implicits to avoid name clashes.

This will fail implicit search in the next commit.
SI-4270 Disqualify in scope implicits that are shadowed.

If an expression wouldn't type check explicitly, it shouldn't be
allowed implicitly.

Employs typedIdent, which already does this sort of thing rather well,
instead of continuing to reimplement it in Implicits.

Remove check for non-implicit synonym, which is subsumed by typing an Ident.

Workaround Scaladoc oddity, by using an attributed select when the context
is deficient.
Clarifying deprecation messages for numeric conversions in Predef
Clarifying deprecation for implicit and explicit usage of the x2y's in Predef
rework Future.dispatchFuture a bit to fix bugs / optimize

This fixes a bug where _taskStack could batch a task
into the wrong executor, as previously commented in the
code.

It now uses the _taskStack machinery for the Future.apply
dispatch in addition to callback dispatch, so we can batch
Future(body) as well.

Less significantly, it micro-optimizes by combining some
different closures and Runnable into a Task object, so
there aren't as many objects created when storing and
dispatching a callback. So it saves a bit of memory
and runtime perhaps.
Refactoring and temporary commit before finishing the fix.
Merge branch 'master' into sbt-reflecton-fix
SI-4270 Refactor for efficiency and clarity.

Avoids allocation of the hashset used by shadowing checks when
searching in the implicit scope, and replaces three checks for
`if (isLocal)` with a sprinkling of polymorphism.
Scaladoc class diagrams part 1

This commit contains model changes required for adding class diagrams
to scaladoc. It also contains an improved implicit shadowing
computation, which hides the shadowed implicitly inherited members
from the main view and gives instructions on how to access them.

This is joint work with Damien Obrist (@damienobrist) on supporting
diagram generation in scaladoc, as part of Damien's semester project
in the LAMP laborarory at EPFL.

The full history is located at:
https://github.com/damienobrist/scala/tree/feature/diagrams-dev

Commit summary:

 - diagrams model
   - diagram settings (Settings.scala, ScalaDoc.scala)
   - diagram model object (Entity.scala, Diagram.scala)
   - model: tracking direct superclasses and subclasses,
     implicit conversions from and to (ModelFactory.scala)
   - diagram object computation (DiagramFactory.scala, DocFactory.scala)
   - capacity to filter diagrams (CommentFactory.scala,
     DiagramDirectiveParser.scala)
   - diagram statistics object (DiagramStats.scala)
   - delayed link evaluation (Body.scala, Comment.scala)
   - tests

 - improved implicits shadowing information
   - model shadowing computation (ModelFactoryImplicitSupport.scala,
     Entity.scala)
   - html generation for shadowing information (Template.scala)
   - tests

Also fixes an issue reported by @dragos, where single-line comment
expansion would lead to the comment disappearing.

Review by @kzys, @pedrofurla.
Scaladoc class diagrams part 2

This commit contains the svg diagram generation using the graphviz
package, the template changes, the css styling and javascript code
that enables displaying and interacting with the diagrams.

The full history is located at:
https://github.com/damienobrist/scala/tree/feature/diagrams-dev

The diagrams are included as svg markup inside the html code. This
enables interacting with the image beyond what would be possible
with a static image (highlighting, scaling, tooltips, links to
nodes, etc).

The svg generation has four main phases: model => dot,
dot => svg (using the graphviz package), svg postprocessing,
inclusion in the html page.

This commit also fixes SI-5212 - links to individual pages
automatically load the left navigation panel of the website.

Commit summary:

 - diagram generation
   - model => dot (DotDiagramGenerator.scala, DiagramGenerator.scala)
   - dot => svg (DotRunner.scala)
   - svg post-processing (DotDiagramGenerator.scala)
   - svg inclusion in the html (Template.scala)

 - diagram interaction
   - css, js and image files

Review by @heathermiller, @kzys.
Documented SyncVar

Since we used it in the DocRunner and noticed it could have better
documentation.

Review by @heathermiller.
Adding backticks to code in deprecation messages in Predef
More fixups.
Adding JDK7 friendly build with new partialdist(-opt) tasks.

* When running in JDK 7 issues a warning.
* New partialdist, partialdist-opt tasks allow creating a distribution with no source/docs.
CPS: enable return expressions in CPS code if they are in tail position

Adds a stack of context trees to AnnotationChecker(s). Here, it is used to
enforce that adaptAnnotations will only adapt the annotation of a return
expression if the expected type is a CPS type.

The remove-tail-return transform is reasonably general, covering cases such as
try-catch-finally. Moreover, an error is thrown if, in a CPS method, a return
is encountered which is not in a tail position such that it will be removed
subsequently.
Remove stray comment
Merge pull request #713 from havocp/havocp-task-stack

Fixups to Future task stack
Removing erronous quoting of implicitNotFound
Fix for broken forwarder.

Wow, I wonder what the upper bound is on how long I might have chased my
tail before finding this. I know what the lower bound is, unfortunately.
It's just that usually the answer to a mystery is not "the empty package
class has magically become the root class, but only sometimes."
Fix for java parser edge case.

Empty statements are A-OK.  Closes SI-5910.  Review by @dragos.