Fixes issue 232

Fixes issue 232 that occurs in at least bash v4.2.25 where "nvm ls" returns "N/A" no matter how many versions of node have been installed.  The fix uses a combination of the find, tr and basename commands instead of basename only.  Tested in bash v3.2.48 and v4.2.25 and zsh v4.3.11.
Updated fix for issues #232 and #244

Fixes issues #232 and #244 where "nvm ls" returns inconsistent results depending on the number of node versions installed.  This updated fix uses the find and sort commands only.  Tested in bash v3.2.48 and v4.2.25, and zsh v4.3.11.
Merge pull request #236 from donovanjamesking/master

Fixes issue 232 and "nvm ls" returning "N/A" when it shouldn't