add a var "ZSH_THEME_SVN_NUVC_IN_DIRTY"

this var control that if the column not under version control was
regarded as dirty data.
bug fixed.

echo error msg when $ZSH_THEME_SVN_UNVC_IN_DIRTY not set
add $SVN_DIRTY_COUNT to display count of dirty
change method that tell if cwd is a working copy

tell if cwd is a working copy according to 'svn status', not to '.svn'