THRIFT-2513 clean up enum value assignment
Patch: Dave Watson

This closes #88

Summary:
Clean up how enum values are handled if an integer value is not
explicitly specified in the thrift file.

For example, the following used to be a compile error, but
works now:

  enum MyEnum {
	SOMEVALUE
  }
  struct MyStruct {
	1: MyEnum e = SOMEVALUE
  }

This change also cleans up some of the error handling with out-of-range
values.  Previously thrift simply issued a warning for enum values that
didn't fit in an i32, but serialized them as i32 anyway.  Now
out-of-range enum values result in a compile failure.

Test Plan:
Included a new unit test to verify the assignment of enum values.  I
also verified that g++ makes the same enum value assignments when
compiling these enums as C++ code.
diff --git a/lib/cpp/test/Makefile.am b/lib/cpp/test/Makefile.am
index c1fad3e..e68e66b 100755
--- a/lib/cpp/test/Makefile.am
+++ b/lib/cpp/test/Makefile.am
@@ -20,6 +20,8 @@
 noinst_LTLIBRARIES = libtestgencpp.la libprocessortest.la
 nodist_libtestgencpp_la_SOURCES = \
 	gen-cpp/DebugProtoTest_types.cpp \
+	gen-cpp/EnumTest_types.cpp \
+	gen-cpp/EnumTest_types.h \
 	gen-cpp/OptionalRequiredTest_types.cpp \
 	gen-cpp/DebugProtoTest_types.cpp \
 	gen-cpp/ThriftTest_types.cpp \
@@ -65,7 +67,8 @@
 	TFileTransportTest \
 	UnitTests \
 	link_test \
-	OpenSSLManualInitTest
+	OpenSSLManualInitTest \
+	EnumTest
 # disable these test ... too strong
 #       processor_test
 #	concurrency_test
@@ -112,6 +115,13 @@
   -l:libboost_unit_test_framework.a \
   -lz
 
+EnumTest_SOURCES = \
+  EnumTest.cpp
+
+EnumTest_LDADD = \
+  libtestgencpp.la \
+  $(BOOST_ROOT_PATH)/lib/libboost_unit_test_framework.a
+
 TFileTransportTest_SOURCES = \
 	TFileTransportTest.cpp
 
@@ -233,6 +243,9 @@
 gen-cpp/DebugProtoTest_types.cpp gen-cpp/DebugProtoTest_types.h: $(top_srcdir)/test/DebugProtoTest.thrift
 	$(THRIFT) --gen cpp:dense $<
 
+gen-cpp/EnumTest_types.cpp gen-cpp/EnumTest_types.h: $(top_srcdir)/test/EnumTest.thrift
+	$(THRIFT) --gen cpp $<
+
 gen-cpp/OptionalRequiredTest_types.cpp gen-cpp/OptionalRequiredTest_types.h: $(top_srcdir)/test/OptionalRequiredTest.thrift
 	$(THRIFT) --gen cpp:dense $<