Adding an _arc() terminal entry

[Christoph B. <us...@be...>]

Hi,

I am working on an _arc() terminal entry and during this some questions 
about possible design/features came up:

1. The main issue is about the clipping. In the current implementation, 
the circles are always clipped at the graph boundaries.

* The clipping of the circles must be done inside each individual 
terminal implementation (works e.g. with Postscript, cairo-related 
terminals, SVG and others).
* I would suggest, that the information, whether clipping is necessary, 
and to which rectangle it should be clipped is provided by a 
terminal-independent function.

* Should the circle object support a [no]clip parameter, which can 
control the clipping at the graph border? In the current implementation 
the circle object is useless for marking something around the graph 
boundary (could just be a single dot on the border). This might also be 
implemented as a new value for 'set clip' and could also affect all 
other objects.


As another thing I would suggest two distinct terminal entries _arc() 
and filledarc().

I'm looking forward to your comments and suggestions,
Christoph