Update build file for MC 1.5.2

* Update to use MC 1.5.2 and build 688 of Forge.
* Update the exec call to recompile to fail on error, this way if the javac
	call generates errors, the entire ant build fails rather than going through
	any more steps
* Use reobfuscate_srg, to gain some level of version independence
Updates for Forge build #688

* A couple method names for retrieving block/item names changed
* Access to the 'value' property of configs is now private, so use the
	getString accessor
Merge pull request #1 from duaiwe/mc-1.5.2

Update for Minecraft v1.5.2 & Forge build 688