Rename Gnuplot outputter
closes #3434
Fix for Dirac off-diagonal Jacobian entries.

This is a quick fix for three tests that crash in debug mode so that we
can keep the build page running, I am working on trying to track down
the root cause of the issue.

Refs #668.
Merge pull request #3437 from permcody/gnuplot_rename

Rename Gnuplot outputter
Merge pull request #3442 from jwpeterson/fixup_dirac_offdiag

Fix for Dirac off-diagonal Jacobian entries.
Only compute off-diagonal Jacobian entries if variable has DOFs.

This patch does the proper checking at the
ComputeDiracThread::onElement() level rather than the
DiracKernel::computeOffDiagJacobian() level, and undoes the quick fix
I committed earlier.

Refs #668.
Fix misc. warnings

Refs #1777.
Merge pull request #3444 from jwpeterson/fixup_dirac_offdiag

Only compute off-diagonal Jacobian entries if variable has DOFs.
Merge pull request #3445 from jwpeterson/fix_warnings

Fix misc. warnings
Fix sign error in the first spline derivative (#3426)
Merge pull request #3453 from dschwen/splinebug_3426

Fix sign error in the first spline derivative
Delete unused variable lines as requested by Cody.

Refs #1777.