Revision 1878413

autogen.sh: Remove per SWIG bindings checked files on release mode.

The .swig_pl_checked, .swig_py_checked, .swig_rb_checked files are
created by 'make -f autogen-standalone.mk autogen-swig' if this script
run on release mode, however they should not exist before users run 
the configure script.

* autogen.sh
  Remove .swig_pl_checked, .swig_py_checked, and .swig_rb_checked files
  after generating SWIG language bindings source files when the script
  runs on release mode.