Adding ability to customize whether the NodalFloodCount threshold
check is a less-than or greater-than check.

By default, it is less-than.
Delete commented-out line.
Use MooseSharedPointers for the file handles.
Avoid multiple lg(N) lookups of the file handle.
Add one more comment.
Delete unnecessary parens.

Add/clarify comment.
Rename variable bubble_it1, there is no bubble_it2...
Able to get the list of all boundary node ids.
WIP. This patch requires bnd_node_iterator fixes...
Removing getBoundaryNodeRange() code.
Intersection with boundary is detected.
Store whether or not a bubble intersects the boundary in the BubbleData object.

Add up all bubble volumes which intersect the boundary.
Compute total area of domain, but why is it 1?
Compute the total intersecting volume on a per-variable basis.
Add comment.
Remove unused variable.
Compute the total volume intersecting the boundary while summing other volumes.
Declare, increment bubble_counter index inline.
Adding ImageMesh class which builds a mesh based on the size data from
an image file specified by the user.

Remarks:
* This currently works for a single image in 2D, but could be extended
  to work on a stack of images in 3D.
* Can scale the 2D domain to a max dimension of 1, 'scale_to_one=true'.
* User can specify a cells_per_pixel value <= 1 to undersample the image.

Refs #3976.
Comment out some print statements, adding flags.