[docs] Enhancements to gettext docs (issue 10536)

Added a minor comment on using the context handler approach for opening a file in example code. http://bugs.python.org/review/10536/diff/1792/Doc/library/gettext.rst File Doc/library/gettext.rst (right): http://bugs.python.org/review/10536/diff/1792/Doc/library/gettext.rst#newcod... Doc/library/gettext.rst:446: fp.close() The fp.close() is not needed, because the context handler exit closes the file (see https://docs.python.org/2.7/library/stdtypes.html#file.close). I fully agree with the change to use the context handler approach for opening the file, and if we use it we should be consequent and rely on it fully. http://bugs.python.org/review/10536/