Hi,

D has the notion of importing modules, whether it is public, private,
or static; basic, selective, or renamed.

This adds support for looking up symbols in both the current and
imported modules so that it is not a necessity to use the qualified
name every time.

Example:

module A;

import B;  // Basic import
import R = C;  // Renamed import
import D : funD;  // Selective import
import E : funR = funE;  // Renamed selective import

void funA()
{
// <- Breakpoint here
}

From the given breakpoint, the following should work in:
- All symbols in module 'A' (our current module) can be looked up by name.
- All symbols in module 'B' can be looked up by name.
- All symbols in module 'C' can be looked up through it's alias R.name.
- Only 'funD' in module 'D' can be looked up by name.
- Only 'funE' in module 'E' can be looked up through it's alias 'funR'.
- All fully qualified symbol names can be looked up.


The implementation of this itself is mostly borrowed from
cp-namespace.c, but differs in the follow ways:
- The separator for modules is a single dot '.'
- Renamed selective imports need special handling for D.


This has a dependency on dwarf2read.c being able to handle language_d
when reading/parsing module/imported declaration symbols, which has
been raised as a separate patch.

Regards
Iain