darcs-2.12.0-2.6

- Update to version 2.12.0 revision 0 with cabal2obs.

- update to 2.12.0
  * `darcs show dependencies`: export patch dependency graph as dot file
  * improvements in `record` output with irrelevant files
  * `darcs log -v --machine-readable`: show internal representation of
  patches (including explicit dependencies). Remove patch viewing via the
  `annotate` command.
  * `whatsnew -s` (and `status`) show conflicting files
  * honor "quiet" flag in command outputs
  * a single `show patch-index` command
  * remove deprecated aliases of show
  * handle file moves natively when importing from git
  * require GHC 7.6 (base > 4.6) and support GHC 8
  * switch to sandi from dataenc
  * remove hack to enable arbitrary protocols via env variables
  * fixed the following bugs:
  +  1807: clarify help of PAGER, DARCS_PAGER
  +  2258: improve patch index error message with suggestion
  +  2269: push hijack test to suspend time
  +  2276: Keep track of patch hijack decisions
  +  2138: report conflicting files in whatsnew -s
  +  2393: remove whatsnew functionality from annotate
  +  2400: use async package to keep track of unpack threads
  +  2459: fall back to writing the file if createLink fails
  +  2479: root dir most not be among the sources of a move
  +  2481: expose API for 'darcs diff' command
  +  2486: obliterate --not-in-remote -q should be more quiet
  +  2489: dequote filepaths while importing from git
  +  2494: output of darcs record with file arguments

- Add missing build dependency on libcurl

- darcs generated by st2obs