Add omxCheck...() statements to demos

We think the bug mentioned earlier has been fixed in r826, but we won't know for sure until omxCheckCloseEnough() are added.

I think I understand the question. omxCloseEnough() takes three arguments: omxCheckCloseEnough(a, b, epsilon = 10^(-15)). 'a' is a numeric vector or matrix, 'b' is a numeric vector or matrix, and 'epsilon' is the maximum allowed difference between the elements of 'a' and the elements of 'b'. You can run mx 1.0 from OpenMx using the function omxOriginalMx(), which takes two arguments: 'mx.filename' is a string that is the name of the mx script to run, and 'output.directory' is a string that is the name of the directory where all the output files will be dumped. Both parameters must have relative paths to the current working directory. Also you must have 'mx' appear somewhere in your $PATH. It's ok to use omxOriginalMx() to get the correct values for omxCloseEnough(). It's not ok to use omxOriginalMx() in either the demo or models/passing scripts. We do not assume that our developers or users have installed Mx 1.0.

The mx-scripts cannot go in "/trunk/demo/mx/" because the R build system will complain if it locates files in the demo directory tree that are not R files. But feel free to place them in a /trunk/inst/mx directory, as files and directories in the inst directory tree are put in the binary release. If you include large data files, keep in mind that you are increasing the size of the binary release (although text files are compressed fairly well in .zip or .tar.gz format).