[REG2.064] Issue 11863 - std.conv.to!string(int/uint, radix) returns incorrect string

https://d.puremagic.com/issues/show_bug.cgi?id=11863

It looks like that the root issue was [incomplete fix](https://github.com/D-Programming-Language/dmd/pull/920) of [bug 8016](http://d.puremagic.com/issues/show_bug.cgi?id=8016) (generate wrong code for nested functions, and corrupt its frame pointer in runtime).
But the bug had been hidden by redundant instantiation of templates (currently it could be done by -allinst switch).