PERF: Parallel streamline was slow. Fixed.

vtkPStreamTracer was causing the creation of a new locator at
every iteration (task), which is very slow for cell locators
since they have to bin data every time. Fixed by removing
the reallocation and using one locator. The input data does not
change between iterations so recreationg the locator was totally
unnecessary.

Change-Id: I966f25caf2e05ba08355a426f3e31f1ac66517ef
ENH: Provide PlaybackFile for recorded interaction events

Many of the Widget tests supply in-code event logs. This patch adds
an additional option to vtkTesting::InteractorEventLoop. The new
option, --PlaybackFile, supplies a file name for the
InteractionRecorder. This allows tests to modify the playback
events without changing the source code for the test. This separates
changes to the playback events from changes to the test code.

A couple of tests have been modified to illustrate the usage of the
InteractorEventLoop.

In the future, the current widget tests should be changed to use the
InteractionEventLoop rather than ifdef'ed code for playing and
recording.

Change-Id: I6aa2afd7c161fe82646fc1df7d326ca8a3249a2f
Merge topic 'fix-locator-recreation' into master

f82238ed PERF: Parallel streamline was slow. Fixed.
Merge topic 'RestoreInteractionWidgetTests' into master

eb1a585d ENH: Provide PlaybackFile for recorded interaction events
Add reader/writer for NIFTIv1 and NIFTIv2 files.

This patch adds support for reading and writing NIFTI files, as well
as full access to the NIFTI header.  Versions 1 and 2 of the NIFTI
header are supported, and the reader can also be used to read Analyze 7.5
files, though the only Analyze header elements that are supported are the
ones that overlap with NIFTI.  Automatic compression and expansion for
gzipped files is also provided whenever the filename ends with a .gz
extension.

Change-Id: Iead3afb1a65d8c01aa52f3ca55c6da2f08703375
Merge topic 'nifti' into master

e7aa61da Add reader/writer for NIFTIv1 and NIFTIv2 files.