Default value for optional coupling

[friedmud]

We've talked in the past about doing something better for optional coupling (like #1483 ) - but I think I have a better idea.

Right now we provide a default value for all other kinds of parameters... why not for optional coupling? So it would look like this:

params.addCoupledVar("name", 3.0, "Documentation");

Then - if that coupling is not set up in the input file then that "variable" will automatically get a value of 3. So in the constructor you would just do this:

_var_value(coupledValue("name"))

And it would either give you the value of the coupled variable or 3....

We could either deprecate the old syntax ( addCoupledVar("name", "Docs") ) or we could leave it and it just implies 0.

[friedmud]

In b9491b2:

Initial commit of optional coupling refs #2358

[friedmud]

In a3b2947:

guard a libmesh call better refs #2358

[permcody]

In b0eeeed:

Fix memory leaks... refs #2358

[permcody]

In b1baaf7:

Initialize _max_qps - refs #2358

[permcody]

In f3b4be0:

More bugs! (Were you a little bit too involved with Game of Thrones?!) - refs #2358

[friedmud]

In 715c5e0:

fixup second order test with new error message refs #2358

[friedmud]

In c689b96:

Fixup Actions that weren't registered properly that caused issues with finding the maximum number of qps closes #2378 refs #2358

[friedmud]

In f0c0460:

make coupled() return a unique index for unsupplied optionally coupled variabes refs #2358