[xdebug-general] Another performance enhancing patch

Just keeping the mailing list in the loop; I submitted another pull
request. This one removes the coverage_line hashes and replaces them
with a flat array. It's a lot more code than the other patches, and
doesn't help performance as much beyond the existing patches; but it
shaves another 4% off of a coverage run.

Running PHPUnit 3.4.15 on a subsuite of my employer's tests with HTML coverage:
Previous 3 patches combined: 37% faster
Replace use_lineno_index with the new coverage_line_array: 41% faster

Keep in mind that a good chuck of time is spent by PHPUnit generating
the HTML report itself, so this can only go so low. :)

https://github.com/derickr/xdebug/pull/5

-- 
taa
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