…sages.

The method wasn't using any `self` data from Context, so it seemed
miseading to implement it as a method.

Macro expansions produce code tagged with debug locations that are completely different from the surrounding expressions.  This wrecks havoc on debugger's ability the step over source lines.

In order to have a good line stepping behavior in debugger, we overwrite debug locations of macro expansions with that of the outermost expansion site.

…woerister

Fix debug line number info for macro expansions.

Macro expansions result in code tagged with completely different debug locations than the surrounding expressions.  This wrecks havoc on debugger's ability the step over source lines.
This change fixes the problem by tagging expanded code as "inlined" at the macro expansion site, which allows the debugger to sort it out.
Note that only the outermost expansion is currently handled, stepping into a macro will still result in stepping craziness.

r? @eddyb

…chton

Various refactorings in the rustdoc module.

None

rustc_trans: do not generate allocas for unused locals.

This fixes a regression observed in a [`mio` test](https://travis-ci.org/carllerche/mio/jobs/152142886) which was referencing a 4MB `const` array.
Even though MIR rvalue promotion would promote the borrow of the array, a dead temp was left behind.
As the array doesn't have an immediate type, an `alloca` was generated for it, even though it had no uses.

The fix is pretty dumb: assume that locals need to be borrowed or assigned before being used.
And if it can't be used, it doesn't get an `alloca`, even if the type would otherwise demand it.
This could change in the future, but all the MIR we generate now doesn't break that rule.

…g, r=alexcrichton

Yield Err in char::decode_utf8 per Unicode, like String::from_utf8_lossy

r? @alexcrichton

Use idiomatic names for string-related methods names.

None