admin: Add documentation for gitmerge.el

* gitmerge.el: New file.
* notes/git-workflow: Add documentation for using it.
epg: Use epg-context-set-*-callback for extra treatment of args

* epa.el (epa-sign-file, epa-encrypt-file, epa-decrypt-region)
(epa-sign-region, epa-encrypt-region): Use
`epg-context-set-{passphrase,progress}-callback', instead of
`setf'.  This partially reverts commit 9e48a95c (bug#19150).
Reported by José A. Romero L.
Ignore files and fix indentation of else static if in d-mode
Emacs compiles after porting changes from http://cx4a.org/repo/emacs.bzr/regexp
Add flag compilation-do-echo-command
Ignore nil variables in c-backward-over-enum-header() in cc-engine.el
Ignore nil variables in c-looking-at-decl-block() in cc-engine.el