Bug 18614 – dmd source uses bool return inconsistently (true should mean success)

usual convention is that a bool return function should return true on sucess (makes it easy with `assert(run_fun(args))` it's what's also commonly used, eg: core.runtime.Runtime.{intialize,terminate} etc and also on parts of dmd (eg: override bool overloadInsert(Dsymbol s): Return true if successful) however we have these oddities in dmd: ``` // src/dmd/root/response.d:207:22 * Returns: * 0 success * !=0 failure (argc, argv unchanged) */ bool response_expand(Strings* args) ``` (also suspicious (prob historical reasons) because should be false and true, not 0 and !=0) and also these: `Returns true if error` (9 occurrences in dmd source code) we should replace each such example with the correct convention, it's confusing when reading corresponding code (especially caller code). Not a problem to change these since the code is not used outside of this repo

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