fix bug for filename completion when opening hyphen is preceded by blanks
To reproduce, e.g. complete

groovy:000> x = '
Fix 2 problems with Filename completion:
Absolute path completion broken on Windows
path completion adds blank at the end of filenames, which is annoying in groovysh

This copies FileNameCompleter from JLine2.10, possibly one day in the future,
JLine might provided fixes on its own. However having a Groovy-maintained
FileNameCompleter does not hurt.
Merge pull request #203 from tkruse/fix_filename_completer

Fix 2 problems with Filename completion:
Merge pull request #204 from tkruse/fix_filename_completion_blanks

small fix for filename completion in Strings
fix test failures introduced by custom FileNameCompleter