Protect against overwriting match data in elmo-pipe folder-initialize.
Merge pull request #69 from jech/elmo-pipe-match-data-fix

Protect against overwriting match data in elmo-pipe folder-initialize.
Use substring-no-properties if available.
elmo-util.el (elmo-string): Assume first argument STRING is string.
wl-util.el (wl-repeat-string): Refactored.
elmo-nntp.el (elmo-nntp-parse-overview-string): Do not use temporary buffer.  Improve performance.
Use `/=' instead of not+eq for number comparison.
wl-action.el (wl-summary-get-dispose-folder): Minor refactoring.