Assume "Ess queue ell" rather than "sequel" for SQL in Django code and docs

[Daniele Procida]

"Ess queue ell" rather than "sequel" should be preferred because:

• it's more obvious to non-native English speakers
• it's more commonly used

So we need to:

• note this in "Commonly used terms" in writing-documentation.txt
• find and change existing instances of "a SQL" to "an SQL" throughout Django code and docs (both are currently used)

I would like to reserve this ticket for first-time committers who take part in the [​​http://www.djangocon.us/schedule/presentation/7/ Don't be afraid to commit tutorial] and the sprints at [​​http://djangocon.us/ DjangoCon US 2013] in September. However, if you want to tackle this ticket before then, please don't hesitate. Feel free to re-assign it to yourself and do whatever you like to it.

[Marc Tamlyn]

I'm unconvinced about "an SQL"... In believed that abbreviations should take a/an from the unabbreviated form I.e. a structured query language query.

[Tim Graham]

@mjtamlyn - Could you provide a reference? Otherwise, we discussed this at some length in IRC and agreed that the rule is phonetic. Unofficial research: ​http://english.stackexchange.com/questions/5265/an-sql-server-database-schema-or-a-sql-server-database-schema

[Tim Graham <timograham@…>]

In 4d13cc56de46ccfc89e9f1381ba4f194070bbdb7:

Fixed #21035 -- Changed docs to treat the acronym SQL phonetically.

The documentation and comments now all use 'an' to
refer to the word SQL and not 'a'.

[Tim Graham <timograham@…>]

In 180b9955cc8816dba1534257f63c6ce389b10759:

[1.6.x] Fixed #21035 -- Changed docs to treat the acronym SQL phonetically.

The documentation and comments now all use 'an' to
refer to the word SQL and not 'a'.

Backport of 4d13cc56de from master