add auto-find-java-and-TC to root build.bat, put jdk\bin on path
add choice.bat (drop-in for the choice cmd which doesn't exist on XP anymore)
fix scripts: don't recompile tc-apis for each plugin (in dist); build scripts do not assume to be invoked in certain working dir
make root `build.bat jdoc` callable from within any dir
use javac @argfiles for root build