Issue #1234 - Remove 'CString' From 'ToLowerString()'

src/plugin/PluginUtil.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2015 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 15 matching lines @@
 std::wstring GetLocationUrl(IWebBrowser2& browser);
 
 template<class CharT, class Traits, class Alloc, size_t N>
 bool BeginsWith(const std::basic_string<CharT, Traits, Alloc>& s, const CharT(&beginning)[N])
 {
   return 0 == s.compare(0, N - 1, beginning);
 }
 
 /**
  * Return a lower-case version of the argument string.
- * Current version uses 'CString::MakeLower()' to preserve legacy behavior during refactoring.
+ * Collates according to the current locale.

[sergei, 2015/12/16 10:32:45]

That seems to be correct choice. We can also create something like
`ToLowerStringCLocale` which we can use to convert HTML tags, for example.

[Eric, 2015/12/16 13:53:26]

For my purposes in this change set, it's the choice that doesn't change the
previous behavior. Right or wrong isn't the question at the moment.

Now, however, its behavior is documented now so that we can make informed
decisions about locale issues in the future.

+ * May not lower-case entire string if it contains embedded null characters.

[sergei, 2015/12/16 10:32:45]

I know that it can theoretically happen, especially because we do store the
entire string while we are converting BSTR which is good, but does it actually
happen and when? 

See the comment for the body.

[Eric, 2015/12/16 13:53:26]

I don't think we ever have a situation where we'll see an input with embedded
null. That said, it's important to document the function as it stands, not how
it's used.

I've changed this specification comment to make fewer guarantees in this
situation.

  */
 std::wstring ToLowerString(const std::wstring& s);