Done-with: Erik Verbruggen

Task-number: QTCREATORBUG-1776

Previously, it would still fail if a forward declaration and declaration
for a class were in the same file.

Task-number: QTCREATORBUG-20

If it encounters a forward declaration, it tries to find the class
declaration globally now.

Task-number: QTCREATORBUG-20

It introduced at least one new crash to do with recovering from parsing
errors.

Reviewed-by: Roberto Raggi

In preparation for finding macro uses.

* Macro: add offset and length
* MacroUse: add line
* Document: add convenience functions for finding a macro definition, use
  or undefined use at a given location.

Reviewed-by: Erik Verbruggen

Encapsulate the details.

Now, the ASTVisitor constructor takes a valid reference to a TranslationUnit.

Done with Erik Verbruggen

Ensure the code model receives file names with clean paths ('/')
and fix paths in the relevant places of the code model. Pass on clean
paths from Cpp reference find and display them correctly in the search
window tooltip.

Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>

updateModifiedFiles ckecks the timestamp and reparses all the modified files in the current snapshot.