Matrix multiply examples/solutions missed dependency on header files

The Makefiles for the matrix multiply examples and solutions didn't
include the dependency between some of the C/C++ files and the header
files. Fixed.

Also fixed an issue with erroneously including the -lrt library flag on
Mac OS X for the pi example/solution.
Add a routine for printing a matrix

Useful for debugging.
Prototype for new print matrix routine

Useful for debugging.