xbps-uhelper: added 'real-version' action.

- This prints to stdout the version of an installed "real" package,
  not virtual. The 'version' action can be used to match any "real" and
  "virtual" package instead.
- Drop strcasecmp() to check actions and use strcmp() instead.
configure: bump to 0.26.1.
NEWS: prepare for 0.26.1.
Merge branch '0.26.x'