fixed the bug that if g:vimshell_data_directory was set to ~/.vim/.cache/vimshell,
it will make an '~' directory under each directory where vim was executed.
Merge pull request #143 from ihacklog/master

fixed the bug that if g:vimshell_data_directory was set to ~/.vim/.cache/vimshell, it will make an '~' directory under each directory where vim was executed.