Rewritten to cache iconv conversion descriptors. On at least some Unix

Rewritten to cache iconv conversion descriptors. On at least some Unix

2002-01-21  Jeffrey Stedfast  <fejj@ximian.com>

	* glib/gconvert.c (open_converter): Rewritten to cache iconv
	conversion descriptors. On at least some Unix systems like
	Solaris, iconv_open() must dlopen the necessary charset modules in
	order to setup the descriptor. This can take a major toll on
	performace if you are constantly opening and closing conversion
	descriptors for the same charset conversions over and over.
	(g_convert_with_fallback): Use close_converter() rather than
	g_iconv_close() since open_converter() now caches iconv
	descriptors.