Update for Minecraft v1.5.2 & Forge build 688

Updates the build file to build against forge build #688, for MC 1.5.2. This will also make the compile target fail if the exec call to recompile.{bat|sh} returns a non-success code. So any errors found by javac will kill the build immediately, rather than going through all the reobfuscate trouble.

Most of the code changes were fairly straightforward, some minor method name changes and using getters/setters instead of accessing private fields.