.gitignore and minimum Git version

[Paul Eggert]

The first attached patch (recently applied to master) isn't needed for 
current versions of git, since the existing patterns 
lisp/**/*cus-load.el and lisp/**/*loaddefs.el subsume the newly added 
patterns.  Looking at the Git release notes, it appears that 
.gitignore's "**" feature was added in Git 1.8.2 (March 2013), so I 
guess Lars is using an older Git version and "**" didn't work for him.

Which raises the issue: what should be the minimum version of git that 
we assume for Emacs developers?  I suggest that we assume Git 1.7.1 
(April 2010) or later, as that's the oldest Git that is still likely to 
be in widespread use -- it's shipped with CentOS 6, for example.

One more thing: as I understand it, the .gitignore patch is needed on 
emacs-24 just as much as on master, and we're doing gittish stuff on 
both branches for now, so this sort of change should be applied to 
emacs-24 and later merged to master.  I attempted to address this by 
applying the second attached patch to the emacs-24 branch; this will 
need to be merged into the master .gitignore in due course.

emacs.diff
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0001-.gitignore-Avoid-as-it-requires-Git-1.8.2-or-later.patch
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