Configure: do not die if live555 version is too old, just warn about it

If you --enable-live555 and are too old, it will error
Else, if you are too old, it will error

If you use live555-tree, you are on your own.

configure.ac

@@ -1748,12 +1748,14 @@ if test "${enable_live555}" != "no"; then
          #endif
          #endif],
         [AC_MSG_RESULT([no])
+          if test "${enable_live555}" == "yes"; then
             AC_MSG_ERROR([Your version of liveMedia is too old: you may get a more recent one from http://www.live555.com/liveMedia.
 lternatively you can use --disable-live555 to disable the liveMedia plugin.])
+          else
+            AC_MSG_WARN([Your version of liveMedia is too old: you may get a more recent one from http://www.live555.com/liveMedia.])
+          fi
         ],[
           AC_MSG_RESULT([yes])
-	 ])
-    ])
           other_libs="-lgroupsock -lBasicUsageEnvironment -lUsageEnvironment"
           other_libs_pic="-lgroupsock_pic -lBasicUsageEnvironment_pic -lUsageEnvironment_pic"
           if test "${SYS}" = "mingw32"; then
@@ -1763,6 +1765,7 @@ lternatively you can use --disable-live555 to disable the liveMedia plugin.])
             # add ws2 for closesocket, select, recv
             other_libs="$other_libs -lws2"
           fi
+
           dnl We need to check for pic because live555 don't provide shared libs
           dnl and we want to build a plugins so we need -fPIC on some arch.
           AC_CHECK_HEADERS(liveMedia.hh, [
@@ -1778,8 +1781,11 @@ lternatively you can use --disable-live555 to disable the liveMedia plugin.])
           ],[
            AC_MSG_WARN([The development files for liveMedia (live555) can't be found])
           ])
+
           CPPFLAGS="${CPPFLAGS_save}"
           AC_LANG_POP(C++)
+        ])
+      ])
   else
     AC_MSG_CHECKING(for liveMedia/libliveMedia.a in ${with_live555_tree})
     real_live555_tree="`cd ${with_live555_tree} 2>/dev/null && pwd`"