add 'doc' command for groovysh
Incorporated review comments from Andre Steingress
GROOVY-6150: small tweaks, new tests
fix a test fail, clean code a bit
do not depend on a version of Java SE
Merge pull request #184 from tkruse/fix-groovysh-test

fix classCastEception in test
GROOVY-4663: fixed test-case on linux
Merge pull request #185 from andresteingress/master

GROOVY-4663: fixed test-case on linux
Merge pull request #182 from masatonagai/feature/groovysh_doc_command

GROOVY-6150: Add 'doc' command to groovysh
Groovysh Tests independent of IO
Due to continued mysterious failures on CI server.
Test cases still remain valid regression tests, i.e. they still
fail if the original change in c1f31183c444b is undone.