Added support for Snow Leopard in Info.plist

seems to work fine when compiling on Mac OS X 10.8 with MacPorts IF
the following is respected:

1) compile all software not installed with MacPorts with:

	export MACOSX_DEPLOYMENT_TARGET=10.6

2) use a clean macports setup and make sure the following Macports files
are modified BEFORE installing MacPorts packages:

	/opt/local/etc/macports/macports.conf: add to the end of the file
		buildfromsource always
		macosx_deployment_target 10.6

	/opt/local/share/macports/Tcl/port1.0/portconfigure.tcl: modify
		configure.ldflags to
		default configure.ldflags   {"-L${prefix}/lib -Wl,-headerpad_max_install_names"}
Small bugfix for implicit declaration warning