Allow Thrift to be built without the Python library.

- Modify configure.ac to check for Python conditionally, like we do for
  Java, Mono, and Erlang.
- Modify Makefile.am to add "py" to SUBDIRS only if Python was detected.


git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@666488 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/test/Makefile.am b/test/Makefile.am
index bf5a0d7..e34e033 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -1,9 +1,13 @@
-SUBDIRS = py
+SUBDIRS =
 
 if ENABLE_JAVA
 SUBDIRS += java
 endif
 
+if ENABLE_PYTHON
+SUBDIRS += py
+endif
+
 noinst_LTLIBRARIES = libtestgencpp.la
 libtestgencpp_la_SOURCES = \
 	gen-cpp/DebugProtoTest_types.cpp \