Multiple directory support in source generators

Routes and templates source generators previously could only generate
sources for one directory at a time.  The problem is, if there were
multiple source directories, there would only be one generated
directory, and they always scanned the generated directory in order to
delete generated files that no longer had source equivalents.  This
meant there was a race condition, because source generators run in
parallel, if a generated file was found but the header hadn't been
written, it would be deleted.

This fixes it to ensure that each source generator only needs to run
once, so projects with multple source directories (eg, the documentation
project) don't have this race condition.

Also made routes generated source handling more robust.
Added a paragraph in relation to db connection pool sizes and thread pool sizes.
Merge pull request #1538 from wsargent/1538-change-ScalaDependencyInjection-page

[doc] Make ScalaDependencyInjection have examples, proper formatting
Merge pull request #1474 from jodyfanning/master

Remove note about incrementalAssetsCompilation
add play2-sprites to modules in documentation

play2-sprites is an sbt plugin that generates sprites from images
made it possible to retreive the internal jdbc connection composed by AutoCleanConnection. Fixes #1543
applied scalariform-format
Change Typesafe repository used for publishing
When packaging, using env var to provide Play version to build command
Prevent Root and Play-Repository projects being published with publish-signed task
Update package script to get API docs from play-docs project
Remove unused import of PgpSettings from Build.scala
Merge pull request #1512 from jroper/action-builder

ActionBuilder docs and improvements
Merge pull request #1547 from jroper/source-generator-multidir

Multiple directory support in source generators
Fixed less compiler error handling

Fixes #1541.

It seems that the errors passed to the callback that takes the Less AST
can be more than just Objects.

Added unit tests so that we'll detect this in future.
#1305 Results restructing highlights and updates
Merge pull request #1541 from jroper/1541-less-fix

Less compiler error reporting broken for imported files
Merge pull request #1540 from benmccann/less-1.4.2

Upgrade the less compiler to version 1.4.2
Merge pull request #1554 from jroper/1305-docs

Results restructing highlights and updates
More highlights