Methods to big decimal

https://jira.codehaus.org/browse/GROOVY-4847
	Include methods round and trunc for BigDecimal class.
	modified:   src/main/org/codehaus/groovy/runtime/DefaultGroovyMethods.java
	modified:   src/test/org/codehaus/groovy/runtime/DefaultGroovyMethodsTest.java
	steps in git:
		$ git remote add methodsToBigDecimal https://github.com/groovy/groovy-core.git
		$ git remote -v
		$ git pull methodsToBigDecimal master
		$ git checkout -b methodsToBigDecimal
		$ git status -v
		$ git commit -a -m "Added methods round and trunc to BigDecimal"
		$ git push origin methodsToBigDecimal

		went to https://github.com/romalopes/groovy-core
			clicked in Compare & pull request