Git translation branch policy change: merge with and from stable/2.16

[John Mandereau]

Dear translators and developers,

>From now on, translation branch at the repository on Savannah should no
longer be merged with master and into staging; instead, it should be
merged with stable/2.16.  This will be so until activity on stable/2.16
drops, that is, when changes in documentation cease to be backported, or
when you translators have reached some well-defined goal (for example,
achieve a full translation of some manual), or when 2.16 releases stop.
Unless there is a plan to merge stable/2.16 into master, commits
regarding translations should be backported from translation to staging
branch; I'm taking over this task now, but all people who are used to
merge translation and staging/master (Francisco, Jean-Charles) and feel
comfortable with cherry-picking may do this.

As a consequence, extreme care must be taken when merging translation
branch into stable/2.16: build must be done from scratch in a build
directory separate from source tree.  I take over from this task and
will give notice if I have difficulty doing so frequently enough (say,
twice a week).  Merging translation and stable/2.16 should be done with
the same care.

Best,
John Mandereau