THRIFT-1965 Adds Graphviz (graph description language) generator

Patch: Rodrigo Setti
diff --git a/compiler/cpp/Makefile.am b/compiler/cpp/Makefile.am
index 8a8f394..a70129a 100644
--- a/compiler/cpp/Makefile.am
+++ b/compiler/cpp/Makefile.am
@@ -85,6 +85,7 @@
                   src/generate/t_javame_generator.cc \
                   src/generate/t_delphi_generator.cc \
                   src/generate/t_go_generator.cc \
+                  src/generate/t_gv_generator.cc \
                   src/generate/t_d_generator.cc
 
 thrift_CPPFLAGS = -I$(srcdir)/src