Attempt to fix race condition.

There was a race condition in vtkDataEncoder when terminating all worker
threads. There was a potential that worker threads would terminate just before
the master thread started to wait for them to terminate. This patch addresses
that issue by ensure that no threads can terminate until the master thread
starts to wait for them.

Change-Id: I7c9b7571e03b7d19a30329403d5c4dbfc3c2ad3e
Add release helper script SourceTarball.bash

Port the Utilities/Maintenance/SourceTarball.bash from ITK 4.5.0 to VTK.
Update the URL and tarball names for VTK.

Change-Id: Id78cb69b781d646e0800322b50c2d2dba905124b
Port SourceTarball.bash to run on OS X

Create a compute_MD5 function to abstract the differences between
the Linux "md5sum" tool and the OS X "md5" tool.

Change-Id: I79fdb8347f99a17643a73179bb98dc8c671442b9
Teach SourceTarball.bash to split source and data tarballs

Teach Utilities/Maintenance/SourceTarball.bash to generate separate
archives for the source code, normal data, and large data.  Organize
the archive layout so that they can all be extracted on top of one
another.  Make the data archives extract into <prefix>/.ExternalData
to appear as if the content came with the source tree.

Add .ExternalData/README.rst to document the directory and indicate its
existence.  Change the BUILD_TESTING default to OFF when the file is not
present.  Teach SourceTarball.bash to leave this file out of the source
tarball and put it in the normal data tarball.  With this approach
users can download and build the source with or without the data and
never hit the network for test data by default.

Change-Id: I33007959c87ea60a9b11f49e5f7af351fc2ca9b7
Merge topic 'fix_test_set_get' into master

48341708 Attempt to fix race condition.
Merge topic 'release-add-SourceTarball-script' into master

bf5cf3cf Teach SourceTarball.bash to split source and data tarballs
57399278 Port SourceTarball.bash to run on OS X
360d6c73 Add release helper script SourceTarball.bash
BUG 7589 Fix Mingw Java libraries name

See:
* http://vtk.org/Bug/view.php?id=10969
* http://vtk.org/Bug/view.php?id=7589

Change-Id: Idad20d624d4d23b7401d22b7c7b7b74506a9ff6f
Merge topic 'JavaMingwLibName' into master

a49ec0bb BUG 7589 Fix Mingw Java libraries name