Argument capturing for preg function family in Callgraph

The Callgraph Profiler captures the regular expressions for the preg function family starting with PHP Extension 5.5.8. This simplifies finding regular expression related bottlenecks, either through inefficient patterns or due to high function call counts.

The functions preg_match, preg_match_all, preg_split, preg_replace and preg_replace_callback are instrumented. The captured regular expression is truncated to the first 30 chars.