Add checks for libcurl to ./configure. Picked version 7.16.0 as lowes…

…t requirement because that's the oldest base-install I could find. I assume we can keep lowering that, if people complain.

git-svn-id: https://svn.apache.org/repos/asf/incubator/couchdb/trunk@707856 13f79535-47bb-0310-9956-ffa450edef68

configure.ac

@@ -104,6 +104,10 @@ AC_SUBST(ICU_CONFIG)
 AC_SUBST(ICU_LOCAL_CFLAGS)
 AC_SUBST(ICU_LOCAL_LDFLAGS)
 
+AC_CHECK_CURL(7.16.0)
+AC_SUBST(CURL_CFLAGS) 
+AC_SUBST(CURL_LIBS) 
+
 AC_PATH_PROG([ERL], [erl])
 
 if test x${ERL} = x; then