Description:
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It'd be great to have a version of str_replace()  that can be configured to work 
on a specified number of replacements.

I propose that the function 

mixed strn_replace ( mixed $search , mixed $replace , mixed $subject, int 
$repetitions, [, int &$count ] )

Be created, which would do the same thing as str_replace() but only as many 
times as $repetitions was set to.

See further discussion of the ways this problem is currently solved.

http://stackoverflow.com/questions/1252693/php-str-replace-that-only-acts-on-
the-first-match

I am up for adding this code in as a patch, but it'd be nice to have some 
feedback if this is desired.