Cleared up docs for node operations
Added check in feedforward network op to ensure that weight matrices are
not self-recurrent (this was not detected by the algorithm)
Redefined mint_check as a variadic macro to usefully report function,
line, and file information. As far as I know, this is the only place in
the MINT source where something beyond plain C89 is used (namely, the
__FUNCTION__ gcc extension, and the C99 variadic macro feature).
Small change to "lateral" weights op
Improved network_operate - now spreading rules make more sense