Move running of vcprompt into own function
Fix bug when format string has a trailing '%'

The check for a trailing percent sign would not trigger, because it
checks for the character '0' instead of \0.
update contributor list
Add infrastructure for vcpromptignore
Implement vcpromptignore for svn, git, hg and fossil
Add tests for vcpromptignore
Update docs for vcpromptignore