Description:
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Not sure how this would work, but a small feature that I can see being 
of use is to be able to show how an extension is loaded.

Built-in, ini or dl() I think are the three ways in which an extension 
can be loaded.

Currently (CLI) php -m shows ...

[PHP Modules]
bcmath
bz2
calendar
com_dotnet
Core
ctype
curl
date
dom

Showing something like ...

[PHP Modules]
Built-in    :             : bcmath
php-cli.ini : C:\PHP5\ext : bz2
Built-in    :             : calendar
Built-in    :             : com_dotnet
Built-in    :             : Core
Built-in    :             : ctype
php-cli.ini : C:\PHP5\ext : curl
Built-in    :             : date
Built-in    :             : dom

and something similar for phpinfo()

Also, once this data is available, maybe it could become available via 
get_loaded_extensions().

Maybe as a second optional parameter 

array get_loaded_extensions ([ bool $zend_extensions= false, [bool 
$include_load_reason= false] ] )