Expanded the regex utilized to validate imports in groovysh. GROOVY-6743

Prior to this change, classes/packages that contained digits were not allowed.
GROOVY-6753: groovysh: better error output for loading file with hyphens
Merge pull request #406 from tkruse/groovy6753_groovysh_file

GROOVY-6753: groovysh: better error output for loading file with hyphens
Merge pull request #401 from spmallette/GROOVY-6743

Expanded the regex utilized to validate imports in groovysh. GROOVY-6743
GROOVY-6743: Update copyright in header
GROOVY-6779: Groovysh ":purge all" and ":show all" commands fail

Use property access instead of field access to load closures of functions, so the "do_all" closure can be loaded.