THRIFT-2906 - linking with boost_unit_test_framework made more portable

Client: C++
Patch: Jon Parise

BOOST_TEST_LDADD Makefile variable added and should be used when linking
with boost_unit_test_framework

This closes #333
diff --git a/lib/cpp/test/Makefile.am b/lib/cpp/test/Makefile.am
index 9ab6ba4..8420357 100755
--- a/lib/cpp/test/Makefile.am
+++ b/lib/cpp/test/Makefile.am
@@ -100,7 +100,7 @@
 
 UnitTests_LDADD = \
   libtestgencpp.la \
-  -l:libboost_unit_test_framework.a
+  $(BOOST_TEST_LDADD)
 
 TransportTest_SOURCES = \
 	TransportTest.cpp
@@ -108,7 +108,7 @@
 TransportTest_LDADD = \
   libtestgencpp.la \
   $(top_builddir)/lib/cpp/libthriftz.la \
-  -l:libboost_unit_test_framework.a \
+  $(BOOST_TEST_LDADD) \
   -lz
 
 ZlibTest_SOURCES = \
@@ -117,7 +117,7 @@
 ZlibTest_LDADD = \
   libtestgencpp.la \
   $(top_builddir)/lib/cpp/libthriftz.la \
-  -l:libboost_unit_test_framework.a \
+  $(BOOST_TEST_LDADD) \
   -lz
 
 EnumTest_SOURCES = \
@@ -125,14 +125,14 @@
 
 EnumTest_LDADD = \
   libtestgencpp.la \
-  -l:libboost_unit_test_framework.a
+  $(BOOST_TEST_LDADD)
 
 TFileTransportTest_SOURCES = \
 	TFileTransportTest.cpp
 
 TFileTransportTest_LDADD = \
   libtestgencpp.la \
-  -l:libboost_unit_test_framework.a
+  $(BOOST_TEST_LDADD)
 
 #
 # TFDTransportTest
@@ -188,9 +188,9 @@
 TNonblockingServerTest_LDADD = libprocessortest.la \
                                $(top_builddir)/lib/cpp/libthrift.la \
                                $(top_builddir)/lib/cpp/libthriftnb.la \
+                               $(BOOST_TEST_LDADD) \
                                $(BOOST_LDFLAGS) \
-                               -levent \
-                               -l:libboost_unit_test_framework.a
+                               -levent
 
 #
 # OptionalRequiredTest
@@ -241,16 +241,16 @@
 processor_test_LDADD = libprocessortest.la \
                        $(top_builddir)/lib/cpp/libthrift.la \
                        $(top_builddir)/lib/cpp/libthriftnb.la \
+                       $(BOOST_TEST_LDADD) \
                        $(BOOST_LDFLAGS) \
-                       -levent \
-                       -l:libboost_unit_test_framework.a
+                       -levent
 
 OpenSSLManualInitTest_SOURCES = \
 	OpenSSLManualInitTest.cpp
 
 OpenSSLManualInitTest_LDADD = \
 	$(top_builddir)/lib/cpp/libthrift.la \
-	-l:libboost_unit_test_framework.a
+	$(BOOST_TEST_LDADD)
 
 #
 # Common thrift code generation rules