Improve and redesign test programs + unify their output (ticket #25)
- Move graph related utilities form test_tools.h to graph_test.h.
- Move the contents of graph_utils_test.h to graph_utils_test.cc.
- Rename map_test.h -> graph_maps_test.h.
- Rename digraph_test.h -> graph_test.h.
- Many improvements in the following files:
* digraph_test.cc
* graph_test.cc
* graph_test.h
* graph_maps_test.h
* graph_utils_test.cc
* bfs_test.cc
* dfs_test.cc
* counter_test.cc
- Test programs print messages only if it really seems necessary.
- Remove \file commands form .cc test files.

 @nodes

 label

 0

 1

 2

 3

 4

 5

 6

 7

 @arcs

 		label capacity

 0 	1 	0  	  16

 0 	2 	1 	  12

 0 	3 	2 	  20

 1 	2 	3 	  10

 1 	4 	4 	  10

 1 	5 	5 	  13

 2 	3 	6 	  10

 2 	4 	7 	  8

 2 	6 	8 	  8

 5 	3 	9 	  20

 3 	6 	10 	  25

 4 	7 	11 	  15

 5 	7 	12 	  15

 6 	7 	13 	  18

 @attributes

 source 0

 target 7