The regex pattern to upper-case things containing an `i` had incorrect
escaping (`\\(`...`\\)` instead of `(`...`)`) so `import` didn't get
renamed.
This wasn't detected because there were no `_runme` files for this
testcase, so add rename_camel_runme.php which uses reflection to check
the wrapped PHP classes, functions and constants are all named as
expected.
Also expand coverage of converting to underscore case and add coverage
for converting to lower-camel-case.
Related to #1041.
