THRIFT-731. configure doesn't check for ant >= 1.7

This patch makes configure check for ant version 1.7 or greater.

Patch: Harlan Lieberman-Berg

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@984207 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/configure.ac b/configure.ac
index f6a8a0d..595f870 100644
--- a/configure.ac
+++ b/configure.ac
@@ -86,7 +86,7 @@
 AX_THRIFT_LIB(java, [Java], yes)
 if test "$with_java" = "yes";  then
   AX_JAVAC_AND_JAVA
-  AC_PATH_PROG([ANT], [ant])
+  PKG_CHECK_MODULES([ANT], ant >= 1.7)
   AX_CHECK_JAVA_CLASS(org.slf4j.Logger)
   have_slf4j="$success"
   AX_CHECK_JAVA_CLASS(org.slf4j.impl.SimpleLogger)