Consistent use of term implementation dependent

[jarno@elovirta.com]

DITA 1.2 specification uses multiple different variations of term 
"implementation dependent":

* implementation-dependent
* implementation dependent
* ... implementation determines ...
* implementation may ...
* implementation and/or stylesheet dependent
* ... left up to the implementation

If a consistent term like "implementation-dependent" was used 
everywhere in the specification to describe that a processing is 
implementation dependent, searching for these cases would be easier.

For example, the XSLT specification has a separate non-normative 
appendix which lists all implementation defined features 
<http://www.w3.org/TR/2007/REC-xslt20-20070123/#implementation-defined-features>. 
Also, XSLT uses two different terms, implementation-defined 
<http://www.w3.org/TR/2007/REC-xslt20-20070123/#dt-implementation-defined> 
and implementation-dependent 
<http://www.w3.org/TR/2007/REC-xslt20-20070123/#dt-implementation-dependent>.

Cheers,

Jarno Elovirta