proposal about src/plot.lisp/$sprint



Hello,

I just had a more detailed look on src/plot.lisp/$sprint after I filed a bug report about that 
function. 
A lot of test cases are mentioned there which $sprint doesn't pass. 

So I propose to cut $sprint out of plot.lisp and put it into the stringproc package. Then it can 
easily be fixed by using stringproc/$printf. ($sprint and $printf can be autoloaded at the 
same time.)

After doing this, there only remains one of the mentioned test cases "unfixed":  
(%i15) sprint (["foo bar", "Foo Bar", "FOO BAR"]);
["foo bar","Foo Bar","FOO BAR"] 
(%o15)                    [foo bar, Foo Bar, FOO BAR]

The rest of cases seems to work fine:
(%i26) sprint(42,true,%i,sqrt(2),x,"FOO",12.23e1,12.23b1,etc);
42 true %i sqrt(2) x FOO 122.3 1.223b2 etc 
(%o26)                                42

Volker