git commit message conventions

[Joseph Myers]

Picking up on a point from 
<https://sourceware.org/ml/libc-alpha/2015-06/msg00031.html>:

I propose that we adopt standard git commit message conventions that: the 
first line of a commit message is a short description of the commit, the 
next line is a blank line, and the rest of the commit message is the 
detailed description / rationale for the patch, typically the contents of 
the patch write-up sent to libc-alpha (but likely minus e.g. descriptions 
of how that patch differs from previous revisions, or anything else that's 
only relevant in the mailing list context and not in the revision 
history).

There are of course some changes that are sufficiently straightforward 
that no long description is needed either in the commit message or on 
libc-alpha (e.g. libm-test-ulps regeneration).  But if there's a more 
detailed description it should go in the commit message.

As usual, if committing for someone else then use --author to make them 
the commit author.

-- 
Joseph S. Myers
joseph@codesourcery.com