Fix Issue 5446 - Ddoc doesn't output aliased names

[ghost]

http://d.puremagic.com/issues/show_bug.cgi?id=5446

This is a fix to output aliased symbols when generating documentation. I've tried to make the output look nice but at the same time semantically valid.

I've implemented the prettyPrintDsymbol function for better pretty printing because calling toPrettyChars will print the module name together with the symbol name and in most cases this creates a very noisy output. Instead toPrettyChars is only used when the aliased symbol is from another module, since this is required to output aliases like this:

deprecated alias core.cpuid.vendor vendor; 

Which is better than just deprecated alias vendor vendor since that is ambiguous to the reader.

[yebblies]

This line shouldn't change.

[ghost]

Retesting now.

[ghost]

I forgot to ask @andralex if he's ok with this change, in particular if the way ddoc looks with this change is ok. We can easily amend things of course. :)

[ghost]

I've noticed a small issue w.r.t. templated function aliases:

alias listDir(C) listdir; 

listDir is a templated function. This is a result of a toChars() call on a TemplateDeclaration, toPrettyChars() does a similar thing.

Do any code paths rely on specific behavior for toChars? If not I could change how TemplateDeclaration prints itself. Otherwise I'll have to add checks in ddoc and use:

TemplateDeclaration *td = s->isTemplateDeclaration();
if (td)
    buf->writestring(td->ident->toChars());
else
    buf->writestring(s->toChars());