add test-dump-cache-tree in Makefile

5c5ba73 (Makefile: Use generic rule to build test programs,
2007-05-31) tried to use generic rule to build test programs, but it
misses the file 'dump-cache-tree.c', since its name is not prefixed by
'test-'.  This commit solves this little problem by renaming this file
instead of carrying out an explicit rule in Makefile.

Signed-off-by: Guanqun Lu <guanqun.lu@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -1301,7 +1301,7 @@ endif
 
 ### Testing rules
 
-TEST_PROGRAMS = test-chmtime$X test-genrandom$X test-date$X test-delta$X test-sha1$X test-match-trees$X test-parse-options$X test-path-utils$X
+TEST_PROGRAMS = test-chmtime$X test-dump-cache-tree$X test-genrandom$X test-date$X test-delta$X test-sha1$X test-match-trees$X test-parse-options$X test-path-utils$X
 
 all:: $(TEST_PROGRAMS)