Tag the actual test task and not a later task.  Fixes #692.
support explicit types on lazy vals in definingValName

lazy val x: Project = project has a rather different enclosing tree
 than lazy val x = project.
fix TagsTest test size generator and properly set Tags.All on tag maps
Restore class files after an unsuccessful compilation.

This is useful when an error occurs in a later incremental step that
requires a fix in the originally changed files.

CC @gkossakowski
Add a pending test case for private var declared in a trait.

Added a test-case for an edge case where an introduction of private member
(var in this case) should trigger recompilation of all classes that
inherit from a trait where the member is declared.

The reason is that current encoding of traits make it impossible for them
to declare fields directly so fields are being introduced in classes
inheriting from those traits. Check the test case for details.
Refine `source-dependencies/import` test.

Clarify what `source-dependencies/import` really tests by renaming
it to `source-dependencies/import-package` which better describes
the scope of that test.

Also, introduce analogous `source-dependencies/import-class` test which
tests dependency tracking on imported classes.

The reason why we should distinguish between imported packages and classes
is that incremental compiler doesn't track packages as products of source
files as it does for classes. Therefore, problem with imported classes
is much more tractable than with imported packages.
Added the tl-os-sbt-plugins to the Community-Plugins documentation.
Docs: fix underline length
Docs: fix nightly build/Setup pages for 0.13.0-SNAPSHOT
Docs: change summary: class file restoration after unsuccessful compilation