Add unit-tests for board_copy_deep

This commit adds the units tests mentioned above.  In addition, it also
adds a fix on the error return value from board_copy_deep that was flushed
out using the unit tests.
Rename 'residentPiece' field to 'piece' in piece_t

The 'residentPiece' struct field name was bad for two reasons.
  1) It broke the coding standard by using camel case rather than
    underscore_case
  2) The word 'resident' really added no value to the term, and cluttered
    up lines.

This commit refactors the code by renaming the field to just 'piece'.
Rename 'theBoard' field to 'spaces' to board_t

The 'theBoard' struct field name was bad for two reasons.
 1) It broke the coding standard by using camel case rather than
   underscore_case
 2) The phrase theBoard is redundant and confusing, considering that its
   a field name in a board_t struct.  If that field is the board, what's
   the rest of the struct?

This commit refactors the code by renaming the field to just 'spaces',
since the array field represents the different spaces on the board.
Rename board_t's curMove field to moves_next

This is the third in a series of commits that rename
struct fields to use the underscore_case enforced by the
Coding Standards for this project.
Added resource cleanup to board_copy_deep unit tests
Remove test-stubs for board_destroy

Initially, I was planning on testing the behavior or board_destroy.  The
main behavior I wanted to unit test was the notion that board_destroy NULL-
ifies allocated field pointers once the resources they point at have been
cleaned up.

However, to check this, I'd have to access invalid memory to see if the
pointers were set to NULL.  Obviously not an option.  So the stub functions
for the Board_Destroy test suite were removed in this commit.
Set square_t* to NULL after destroying square_t

The board_destroy function cleans up each square individually.  In order to
prevent other modules from inadvertently using the destroyed struct, this
commit sets each square_t pointer to NULL.

While this doesnt _prevent_ other code from trying to access the destroyed
square_t's, it will make the problem easier to detect by immediately
causing a segfault.
Remove unused variable
Add board_equal and square_equal functions

This commit adds the board_equal and square_equal functions,
which allow boards and individual squares to be compared.
Add file_utils_exists util function

This commit adds the file_utils_exists function, a short wrapper
around a check to determine whether a given C string containing
a filename matches a file on the host filesystem.

Since this was the first general-purpose util function written for
the jegChess project, this commit also adds a little infrastructure
for creating util libraries.  This includes the added utils/ directory,
as well as altering the existing configure.ac and src/Makefile.am files