groovysh: Import command is vulnerable and ugly

to reproduce:

groovy:000> import java.awt.TextField
===> [import java.awt.TextField]
groovy:000> import java.awt.TextField;
===> [import java.awt.TextField, import java.awt.TextField;]

should be just one time textfield

groovy:000> import java.awt.TextField; println('foo')
===> [import java.awt.TextField; println('foo')]
groovy:000> 2+2
foo
===> 4

should be prevented

Also the output of the list of imports is unnecessarily verbose, the "import " prefix does not add information, it just takes away screen space. Ideally this would even reduce package names to one letter, but this is bothersome to parse, given the variants of the import command