change precision EPSILON in C code (#217)

* change precision EPSILON in C code

* change precision EPSILON in C code V2

* change precision EPSILON in C code V3 (add comment and remove unnecessary lines

Author: ncourty

ot/lp/network_simplex_simple.h

@@ -1507,7 +1507,7 @@ namespace lemon {
 			if( retVal == OPTIMAL){
                 for (int e = _search_arc_num; e != _all_arc_num; ++e) {
                     if (_flow[e] != 0){
-                        if (abs(_flow[e]) > EPSILON)
+                        if (fabs(_flow[e]) > _EPSILON) // change of the original code following issue #126
                             return INFEASIBLE;
                         else
                             _flow[e]=0;