[drupal-docs] Documenting PHP requirements

[Gabor Hojtsy]

> How accurate/complete are the OPTIONAL REQUIREMENTS in the install
> instructions with regards to PHP extensions?
> 
> OPTIONAL REQUIREMENTS
> ---------------------
> - To use XML-based services such as the Blogger API, Jabber, RSS
>   syndication, you will need PHP's XML extension. This extension is
>   enabled by default in standard PHP4 installations.
> 
> What about mentioning GD and Mbstring? Are they ever *missing* from PHP4
> (4.3.3 or greater) or PHP5? Are there other extensions that are really
> useful and that we should mention? What extensions do *you* have
> compiled in or turned on?

GD and especially Mbstring can be missing. GD is often enabled on hosts
though, while mbstring is not that popular AFAIK.

Goba